Patent Publication Number: US-2022224679-A1

Title: Authenticated Session Management Across Multiple Electronic Devices Using A Virtual Session Manager

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 16/565,771, filed Sep. 10, 2019, which is a continuation of U.S. patent application Ser. No. 15/395,541, filed Dec. 30, 2016, and issued as U.S. Pat. No. 10,462,124 on Oct. 29, 2019, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     In the era of the Internet of Things, and with the proliferation of many different types of human interface devices and user agents, users may desire to shift a session between devices in a seamless manner. For example, a user may have a smart phone, a tablet computing device, an Internet-enabled television, a home voice assistant and one or more Internet-of-Things-enabled appliances in his or her home. The user may want all such devices to login to a single account at the same time, and operate together as part of a single session. 
     This is not easily possible with current technologies, as web sessions are currently isolated by user agents. For example, when a user initiates a web browsing session, the Hypertext Transfer Protocol (HTTP) used is mostly stateless and treats each request as an independent transaction that is unrelated to any previous request. Thus, the user must be authenticated to each device as the user switches between devices. This can lead to a poor user experience, especially on mobile devices with small user interfaces in which entry of a passcode can be difficult. 
     In the prior art, to maintain a stateful session using the HTTP protocol, authentication cookies are commonly used. Authentication cookies are used by web servers to determine whether the user of a particular device is logged in to a session or not, and to identify the account with which the user has been logged in. However, a cookie is not useful for maintaining a session across multiple devices or multiple hosted services. 
     In addition, in some cases a user may wish to establish or rejoin a session on a device that is not personal to the user. Examples of such devices include public computers in libraries or hotel business centers. However, to preserve the security of the user&#39;s account the user may not wish to enter his or her passcode into a public computer. 
     This document describes methods and systems for securely maintaining a user session across multiple devices. 
     SUMMARY 
     In some embodiments, a web session is maintained for a user across multiple electronic devices. A user agent of a first electronic device that is being used by the user will discovering a second electronic device that is in a communication range of the first electronic device. The user agent will determine that the second electronic device includes a virtual session manager, and it will receive a first authentication request. The first authentication request will include a request to access a first web resource and also a login credential for the user at the first web resource. The first electronic device will transmit the first authentication request to an endpoint device via the virtual session manager of the second electronic device so that the second electronic device can present a grant token to the endpoint device without the first electronic device having any access to the grant token. The user agent will then receive, from the virtual session manager of the second electronic device, a first access token in response to the first authentication request. The first access token has a life that is shorter than a life of the grant token, such that the grant token is relatively long-lived and the first access token is relatively short-lived. The user agent will store the first access token in a memory that is accessible to the first electronic device. The user agent will use the first access token to access the first web resource and establish or maintain a virtual session with the first web resource. 
     In some embodiments, when the user agent receives the first access token from the virtual session manager, the user agent also may receive a history from the virtual session manager. The history will include one or more parameters associated with the user&#39;s use of the first web resource when the grant token was transmitted to the endpoint device. Then, when accessing the first web resource, the user agent may automatically send the parameters to the first web resources to maintain or automatically reconnect to the virtual session so that the virtual session is uninterrupted without manually entering the parameters. 
     In some embodiments, the virtual session manager of the second electronic device may transmit the first authentication request to the endpoint device with the grant token. 
     In some embodiments, the user agent may cause the first electronic device to discovering additional electronic devices that are in the communication range of the first electronic device and that each include a virtual session manager. If so, the user agent may cause the first electronic device to present, to a user of the first electronic device, identifiers associated with each of the discovered additional electronic devices, along with an identifier for the second electronic device. The system may then receive, via a user interface, a selection of the second electronic device with the first authentication request. 
     In some embodiments, upon determining that the second electronic device includes a virtual session manager, the user agent also may receive identifiers for various virtual sessions for the first web resource, each of which has a corresponding grant token. The user agent may cause the first electronic device to present, to a user of the first electronic device, the identifiers for the virtual sessions. The user agent may receive, via a user interface, a selection of one of the virtual sessions. The user agent may cause the first electronic device to transmit, to the endpoint device (optionally via the second device) with the first authentication request, a request to connect to the selected virtual session. The grant token that will be presented to the endpoint device will be the grant token that corresponds to the selected virtual session. 
     In some embodiments, upon determining that the second electronic device includes a virtual session manager, the user agent of the first electronic device also may receive identifiers for a various available virtual sessions for the first web resource, each of which has a corresponding grant token. The user agent may present, to a user of the first electronic device, the identifiers for the available virtual sessions. The user agent may receive, via a user interface, a request to start a new virtual session rather than connect to one any the available virtual sessions of the presented identifiers. If so, then it may identify the grant token as a new grant token for the new virtual session, and store the new grant token in a memory. The virtual session manager of the second electronic device may transmit the request to start the new virtual session to the endpoint device with the first authentication request. 
     The virtual session manager of the second electronic device also may, in response to receiving the request to start a new virtual session, generate a prompt for the user to present an access credential to the second electronic device. The virtual session manager may receive the access credential via a user interface and confirm that the access credential authorizes the user to access the first web resource. In response to receiving the access credential and confirming that the access credential authorizes the user to access the first web resource, the virtual session manager may transmit the request to start the new virtual session to the endpoint device with the first access request. 
     In some embodiments, the user agent of the first electronic device may, when the first authentication token expires or is about to expire, transmit a re-authentication request to the endpoint device via the second electronic device so that the virtual session manager of the second electronic device can present the re-authentication request with the grant token to the endpoint device without the first electronic device having any access to the grant token. The user agent may receive an updated access token from the endpoint device via the second electronic device. The updated access token will replace the first access token and will have a life that is shorter than the life of the grant token. The user agent may then use the second access token to maintain the virtual session. 
     In some embodiments, the virtual session manager of the second electronic device, may present the user an interface via which a user may command the virtual session manager to do one or more of the following: (i) disable the virtual session, in which case the virtual session manager will disable the first access token; (ii) re-enable a disabled virtual session, in which case the virtual session manager will grant an updated access token for the disabled virtual session to all electronic devices for which the virtual session manager previously disabled access; (iii) re-group a virtual session, in which case the virtual session manager will identify an alternate virtual session for which it has a grant token, send the grant token for the alternate virtual session to the endpoint device, receive an alternate access token from the endpoint device, and transmit the alternate access token to the first electronic device so that the first electronic device will replace the first access token with the alternate access token and use the alternate access token to connect to the alternate virtual session; (iv) disable the virtual session, in which case the virtual session manager will disable the first access token and delete the grant token for the virtual session; or (v) remove the first electronic device, in which case the virtual session manager will disable the first access token and prevent the first electronic device from receiving additional access tokens until the first electronic device receives a valid authentication credential. 
     In some embodiments, the user agent may prompt the user to perform a known user action. In response to detecting the known user action, the user agent will obtain a user presence token, and it will transmitting the user presence token to the first web resource with the first access token when establishing the virtual session with the first web resource. This may allow the first web resource to verify the identity of the user. 
     In other embodiments, a method of maintaining a web session for a user across multiple electronic devices includes, by a virtual session manager of a second electronic device, receiving a first authentication request from a first electronic device that is in a communication range of the second electronic device. The first authentication request will include a request to access a first web resource and comprises a login credential for a user of the first electronic device at the first web resource. The virtual session manager will transmit the first authentication request to an endpoint device with a grant token without providing the first electronic device with any access to the grant token. The virtual session manager will receive, from the endpoint device, a first access token in response to the first authentication request. The first access token will: (i) have a life that is shorter than a life of the grant token such that the grant token is relatively long-lived and the first access token is relatively short-lived; and (ii) be configured to grant the first electronic device access to the web resource. The virtual session manager will transmit the first access token to the first electronic device so that the first electronic device can establish a virtual session with the first web resource. 
     Optionally, the virtual session manager of the second electronic device may identify one or more parameters associated with the user&#39;s use of the first web resource at a time when the grant token was previously transmitted to the endpoint device. When sending the first access token to the first electronic device, the virtual session manager also may send the one or more parameters so that the first electronic device can reconnect to the first web resource and establish the virtual session as a continuation of a previous virtual session. 
     Optionally, the virtual session manager of the second electronic device also may provide the first electronic device with identifiers for various virtual sessions for the first web resource, each of which has a corresponding grant token. The virtual session manager may receive a selection of one of the virtual sessions from the first electronic device. It will then transmit, to the endpoint device with the first authentication request, a request to connect to the selected virtual session, wherein the grant token that is presented to the endpoint device is the grant token that corresponds to the selected virtual session. 
     Optionally, the virtual session manager also may: provide the first electronic device with identifiers for a plurality of available virtual sessions for the first web resource; receive, from the first electronic device, a request to start a new virtual session rather than connect to one any the available virtual sessions; and identify the grant token as a new grant token for the new virtual session, and storing the new grant token in a memory of the second electronic device. 
     Optionally, in response to receiving the request to start a new virtual session, the virtual session manager also may generate a prompt for the user to present an access credential to the second electronic device. The virtual session manager may receive the access credential via a user interface and confirm that the access credential authorizes the user to access the first web resource. In response to receiving the access credential and confirming that the access credential authorizes the user to access the first web resource, the virtual session manager may transmit the request to start the new virtual session to the endpoint device with the first access request. 
     Optionally, when the first authentication token expires or is about to expire, the virtual session manager also may receive a re-authentication request from the first electronic device. The virtual session manager may present the re-authentication request with the grant token to the endpoint device without the first electronic device having any access to the grant token. The virtual session manager may receive an updated access token from the endpoint device. The updated access token will be configured to replace the first access token and enable the first electronic device to maintain the virtual session, and it will have a life that is shorter than the life of the grant token. The virtual session manager will transmit the second access token to the first electronic device. 
     Optionally, the virtual session manager may present the user an interface via which a user may command the virtual session manager to (i) disable the virtual session, in which case the virtual session manager will disable the first access token; (ii) re-enable a disabled virtual session, in which case the virtual session manager will grant an updated access token for the disabled virtual session to all electronic devices for which the virtual session manager previously disabled access; (iii) re-group a virtual session, in which case the virtual session manager will identify an alternate virtual session for which it has a grant token, send the grant token for the alternate virtual session to the endpoint device, receive an alternate access token from the endpoint device, and transmit the alternate access token to the first electronic device so that the first electronic device will replace the first access token with the alternate access token and use the alternate access token to connect to the alternate virtual session; (iv) disable the virtual session, in which case the virtual session manager will disable the first access token and delete the grant token for the virtual session; or (v) remove the first electronic device, in which case the virtual session manager will disable the first access token and prevent the first electronic device from receiving additional access tokens until the first electronic device receives a valid authentication credential. 
     In some embodiments, the virtual session manager may receive an identifier of a user action from the first electronic device; and it may determine whether the user action matches an expected action. In response to detecting that the user action matches the expected action, the system may generate a user presence token. The virtual session manager may transmit the user presence token to the first web resource with the first access token. 
     In additional embodiments, a method of maintaining a web session for a user may include, by one or more endpoint devices, receiving a first authorization request. The first access authorization may include a request by a user agent of a first electronic device that is being used by a user to access a first web resource. The first authorization request may include a login credential for the user at the first web resource. The first authorization request may be received from a second electronic device rather than the first electronic device. The endpoint device(s) may determine that the second electronic device includes a virtual session manager for the user and that the virtual session manager includes a grant token. The endpoint device(s) may confirm that the grant token is valid and then transmit a first access token to the second electronic device. The first access token will be configured to grant the first electronic device access to the first web resource. 
     Optionally, when the endpoint device(s) determine that the virtual session manager includes the grant token, the endpoint device(s) may receive the grant token with the first authentication request. 
     Optionally, the endpoint device(s) may receive a re-authentication request and the grant token from the second electronic device and confirming whether the grant token is still valid. If the grant token is still valid, the endpoint device(s) will send an updated access token to the second electronic device. The updated access token will be configured to replace the first access token and enable the first electronic device to maintain access to the first web resource. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of the various entities that make up a system including various hosted services, users, and devices. 
         FIG. 2  illustrates an example of a two-token authentication model. 
         FIG. 3  is a flowchart that illustrates an example process of two-token authentication. 
         FIG. 4  illustrates how a system may implement a two-token model with a variety of user agents, some of which may not support the two-token model. 
         FIG. 5  illustrates an example account manager user interface. 
         FIG. 6  is a flowchart that illustrates an example process of two-token validation with multiple user agents. 
         FIG. 7  illustrates how a virtual session manager may manage authentication of multiple devices and allow the devices to share a single session. 
         FIG. 8  is a block diagram showing example hardware components that may be included in various devices of the system, such as in a user electronic device, a hosted service or an automated initiator. 
     
    
    
     DETAILED DESCRIPTION 
     Terminology that is relevant to this disclosure includes: 
     The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Also, the term “comprising” (or “comprise”) means “including (or include), but not limited to.” The relative terms “long” and “short” are intended to be relative measurements with respect to each other, in that the measurement value of an item that is designated as “long” will be relatively longer than the measurement value of a corresponding item that is designated as “short.” Unless defined otherwise, all technical and scientific terms used in this document have the same meanings as commonly understood by one of ordinary skill in the art. 
     An “access token” is a short-lived token that represents a user&#39;s approval for a user agent to access a web server on behalf of a user. An authentication cookie is an example of an access token. A cookie is a small piece of data that is sent by a website and stored in the user&#39;s web browser while the user is using the browser to access one or more websites. 
     An “electronic device” or a “computing device” refers to a device that includes a processor and memory. Each device may have its own processor and/or memory, or the processor and/or memory may be shared with other devices as in a virtual machine or container arrangement. The memory will contain or receive programming instructions that, when executed by the processor, cause the electronic device to perform one or more operations according to the programming instructions. Examples of electronic devices include personal computers, servers (such as those used in hosted services), mainframes, virtual machines, containers, gaming systems, televisions, and mobile electronic devices such as smartphones, personal digital assistants, cameras, tablet computers, laptop computers, media players and the like. In a client-server arrangement, the client device and the server are electronic devices, in which the server contains instructions and/or data that the client device accesses via one or more communications links in one or more communications networks. In a virtual machine arrangement, a server may be an electronic device, and each virtual machine or container may also be considered to be an electronic device. In the discussion below, a client device, server device, virtual machine or container may be referred to simply as a “device” for brevity. 
     An “endpoint device” is a physical or virtual device or a group of physical or virtual devices that serve as an entry point for event-driven background processing for the grant of access to one or more web resources in a communication network. For brevity, this document may refer to an endpoint device simply as an “endpoint.” Examples of endpoints discussed in this document include a login endpoint and a re-authentication endpoint. 
     A “grant token” is a long-lived authentication token that represents a user&#39;s approval for one or more user agents to access one or more web servers on behalf of the user. A grant token may be stateful (in which case the grant token has a record in a server-side data storage facility) or stateless (meaning that no server-side record exists for the grant token). 
     The term “hosted service” refers to a system that includes one or more electronic devices that will remotely provide or process data or execute programming applications for one or more client electronic devices. A hosted service may be provided in the form of software as a service, platform as a service, or infrastructure as a service. A hosted service may include servers and infrastructure elements (such as operating systems and communication systems) that are dedicated to each client, or it may provide services to multiple clients with shared servers and other resources. Examples of hosted services include web services, email services, other messaging services, cloud data storage services, multimedia content services, social media services and other types of hosted services. In some embodiments, a hosted service may make a group of such services available to a user with a common login and a single user account. 
     The terms “memory,” “memory device,” “data store,” “data storage facility” and the like each refer to a non-transitory device on which computer-readable data, programming instructions or both are stored. Except where specifically stated otherwise, the terms “memory,” “memory device,” “data store,” “data storage facility” and the like are intended to include single device embodiments, embodiments in which multiple memory devices together or collectively store a set of data or instructions, as well as sections within such devices. 
     The terms “processor” and “processing device” refer to a hardware component of an electronic device that is configured to execute programming instructions. Except where specifically stated otherwise, the singular term “processor” or “processing device” is intended to include both single-processing device embodiments and embodiments in which multiple processing devices collectively perform a process. 
     A “user agent” refers to a software agent that is configured to act on behalf of a user of an electronic device to access a hosted service. Examples of user agents include browsers and native applications such as email or messaging clients, streaming media service applications, and cloud storage service applications. 
     A “virtual session manager” is a software application that is configured to run on an electronic device and manage the device&#39;s ability to access one or more remote web services via one or more web sessions. 
     A “web resource” is a remote service that is available from a hosted service in a communication network, such as a website, a cloud-based storage service, or a cloud-based electronic messaging service. 
     The terms “web session,” “virtual session” and “session” synonymously refer to a sequence of request-response transactions to one or more web resources in a communication network that are initiated by a single user. Examples include HTTP request-response transactions in an HTTP session. The requests in a session will be spaced apart in time such that the time between requests does not trigger an inactivity threshold in which the user is required to log into the user&#39;s account again to continue accessing the web resource. 
     A “web token” is a token representing claims to be transferred between two entities. 
       FIG. 1  illustrates various components of systems and relationships between electronic devices that will be discussed in this document. Any number of hosted services  113 ,  114  are available to provide web resources to client electronic devices via a communication network  110 . The communication network  110  may be a local area network (LAN), a wide area network (WAN), a mobile or cellular communication network, an extranet, an intranet, the Internet and/or combinations of any of these networks or other networks. Examples of client electronic devices include a smartphone  102 , a computing device  103  such as the tablet computing device shown, on-board vehicle devices  104  such as in-dashboard entertainment and navigation systems, wearable electronic devices such as a smart watch  105 , and connected Internet of Things devices such as a home voice assistant  106 . 
     In certain embodiments, one or more endpoint devices  112  may be available to receive authentication requests from the electronic devices and issue authentication tokens to the electronic devices using procedures such as those discussed below. 
       FIG. 2  provides a high-level overview of a method of authenticated session management using a two-token model. In the two-token model, two authentication tokens are used to manage a between a session between a user agent  201  of an electronic device and a web resource  202 . When the user agent  201  issues an authentication request for the web resource  202 , it will present a credential to a login endpoint  204 . If the credential is valid (i.e., if it permits the user agent to access the web resource), the login endpoint  204  will establish the session by issuing an access token and a grant token to the user agent  201 . The user agent  201  will store the access token and the grant token in a memory of its associated electronic device. The user agent  201  can then present the access token to the web resource  202  in order to be granted access the web resource  202 . 
     When the access token is expired about to expire, the user agent  201  can send a re-authentication request to a re-authentication endpoint  205 . The re-authentication endpoint  205  may be separate from the login endpoint  204  as shown, or the two endpoint devices may share one or more hardware elements. Upon validating of the re-authentication request, the re-authentication endpoint  205  will return a new access token to the user agent  201  so that the user agent  201  can maintain the session with the web resource  202 . 
     The grant token represents a user&#39;s approval. The grant token has a relatively long life, and optionally an infinite lifetime. A user agent can present a grant token to obtain new authentication tokens. The grant token keeps the user&#39;s approval in the user agent for a relatively long time, unless the user or another entity revokes or invalidates it. In this way, the user does not need to authenticate again and again during that lifetime of the grant token. A grant token may include a timestamp representing its time of creation. The grant token also may include an identifier that the system can use to identify the user who is associated with the grant token (i.e., the recipient of the grant token). In addition, the grant token may include fields such as an address of the re-authentication endpoint, an identifier (such as a session cookie name) for the access token, an expiration time, and/or an address from which an image of the user may be returned. 
     The access token has a relatively short life (i.e., a shorter life than that of the grant token). This shorter life can limit the ability of such tokens to be misused if compromised. The access token may be presented to a web resource to gain access to the web resource. The grant token may not be used for that purpose. 
     This process is further illustrated in the flow diagram of  FIG. 3 . In order to request access to a web resource, a user agent may transmit an authentication request to a login endpoint  301  by transmitting a credential to an address of the login endpoint. The credential can be any credential that the login endpoint can use validate the credential  302  and thus determine whether the user agent is authorized to access the web resource, such as a passphrase, a biometric identifier, a key or any other credential. 
     If the credential is valid (i.e., if it permits the user agent to access the web resource), the login endpoint will establish a session by transmitting an access token and a grant token to the user agent  303 . In some embodiments, the login endpoint may establish the session as an authenticated HTTP session by returning an authentication cookie (whose value is the authentication token) in the set-cookie HTTP header. Other methods of issuing the tokens to the user agent may be employed. Optionally, when the login endpoint returns the grant token and access token to the user agent, the login endpoint also may transmit a uniform resource locator (URL) or other address of the re-authentication endpoint so that the user agent knows the address to which it must send a request for a new access token. 
     The user agent can then transmit the access token to the web resource  304 . The web resource will give the user agent access to the web resource and thus maintain the session  312  so long as the access token is valid and has not expired. 
     When an access token has expired or is about to expire  305  (i.e., within a threshold period of time or other unit of measure from anticipated expiration), the user agent can send a re-authentication request  306  to the re-authentication endpoint to request a new access token. The re-authentication request may include the grant token, or it may include another token that is derived from the grant token. For example, instead of sending the actual grant token the user agent may send a hash-based message authentication code (HMAC) signed by the grant token to indicate that user agent owns the grant token. In some embodiments, the user agent may submit the re-authentication request as an XMLHttpRequest to the re-authentication endpoint, with the grant token in the “authorization” HTTP header. 
     Upon receipt of a re-authentication request from the user agent, the re-authentication endpoint will determine whether the grant token is valid and not revoked  307  using any suitable validation process such as a lookup table or access control list. If the grant token is valid and not revoked  307 , the re-authentication endpoint may return a new access token to the user agent  308  so that the user agent can use the new access token to maintain the session. Otherwise, the re-authentication endpoint will not return a new access token, in which case the session will expire  309  when the original authentication token expires. For example, the re-authentication endpoint may return an error message in the HTTP response body. The user agent will then be required to present a credential again to the login endpoint or the re-authentication endpoint to maintain the session or establish a new session. Also, the user agent may then delete the grant token from its device&#39;s memory. The re-authentication endpoint may also send a “delete grant token” command to a logout endpoint or other server-side location where the grant token has been stored, optionally in association with the user&#39;s profile. 
     Optionally, as a condition returning a new access token, the re-authentication endpoint also may require that the user&#39;s profile data satisfies one or more additional rules  310 . For example, the re-authentication endpoint may access a data storage facility with a profile for the user that is associated with the grant token, examine the data in the user&#39;s profile, and only return the access token if: (i) the user who is associated with the user agent is still signed into an account and not logged out; (ii) the user has not changed its credential since a most recent prior access request; and/or (iii) no known account associated with the user has been flagged as having encountered suspicious activity that may indicate that the account has been compromised. In this way, the re-authentication endpoint will ensure that the grant token is not issued if one or more significant events associated with the user&#39;s account have occurred, such as a login credential change or a potential security compromise. Other rules may require different conditions. 
     The system also may provide for the entry of logout commands, which will expire or revoke grant tokens. For example, a user interface of the first electronic device may permit the user to enter a command to terminate the session, in which case a command to revoke of the grant token will be sent to the re-authentication endpoint and/or a server that contains the user&#39;s profile. The user&#39;s electronic device also may delete the grant token in response to the command. The electronic device also may transmit a command to the re-authentication device and/or a logout endpoint to delete the grant token. 
     In various embodiments, the two-token model described above may use an access token format that matches that of a cookie in a single token model. In this way, if a particular user agent does not support a two-token model, the login endpoint may return only an access token to that user agent, or the user agent may receive a grant token but ignore it.  FIG. 4  illustrates how a two-token model may be used with both two-token complaint user agents and user agents that do not have two-token model support capability. In  FIG. 4 , a web resource  402  may be available to various types of user agents, including a first user agent  401  that is programmed to support a two-token model and a second user agent  421  that does not have such programming and cannot support a two-token model. Each of the user agents  401 ,  421  can request access to the web resource by presenting their credentials to the login endpoint  404 . When the login endpoint  404  receives an authentication request from a user agent, the login endpoint  404  will examine the authentication request to determine whether the user agent supports the two-token model. One way of doing this may be that a two-token model compliant user agent will self-identify that it is two-token model compliant in a header of the authentication request (such as an “Accept-Session-Management” HTTP header). If the login endpoint  404  determines that the user agent is two-token compliant, it will return both an access token and a grant token to that user agent  401 . When the access token expires or is about to expire, the two-token compliant user agent  401  may then use the grant token to submit a re-authentication request to a re-authentication endpoint  405 . If the login endpoint  404  determines that the user agent is not two-token compliant, it will return only an access token, but a not grant token, to that user agent  421 . Each of the user agents  401 ,  421  may use their access tokens to access the web resource  402 . 
     Grant tokens can be stored on the server side and enable a user agent to have multiple sessions active at any point in time. To enable this, any of the endpoints may create and store a session record for each grant token. The session record will include the grant token and information that can be used to distinguish that grant token&#39;s session from other sessions that are associated with the user agent, such as an identifier for the user account, a user agent identifier, time of creation, time of last access, and/or other data. The system also may generate and store data (such as web tokens) with additional data such as the address of the re-authentication endpoint, the name of the access token, an expiration time for the access token, a timestamp when the grant token was issued, an expiration time for the grant token, an email or other address for the user, a name or other identifier to display for the user, and/or an address from which the system may retrieve a digital image file that is associated with the user (such as user image). 
     When a user logs out of a particular session, the endpoint will delete the session record from its memory. A session record also may be deleted in response to an action by an administrator, or if one or more session termination rules have been identified. For example, the endpoint may automatically terminate a session if one or more security-related issues have been identified with the user&#39;s account. Examples of such issues include: (i) the occurrence of a credential change; (ii) or a per-user active session limit having been reached (i.e., that the user is logged into more than a threshold number of sessions at one time; or (iii) detection that multiple user agents associated with a single user are being used in disparate locations at the same time or within a time frame in which the user could not have been in all of the locations during the time frame. 
     In addition, to enable multiple sessions the user agent or the device that includes the user agent may be programmed to include a session manager. The session manager may be a web page or other interface that displays all active grant tokens across a set of user agents. For example, a user (e.g., userl@example.com) who is logged into a website can visit the session manager web page, and view all grant tokens issued by the website in the name of userl@example.com. The session manager also may display additional information for each grant token such as device information, login time, or other details to help the user distinguish the grant tokens from each other. By browsing the session manager, the user may be alerted that he or she neglected to log out of a session on a particular device. Ot, the user may be alerted that his or her account is being used on an unrecognized device. In either case, the session manager may enable the user to terminate a session by providing a user interface that will receive a termination command, in response to which the system will delete the grant token corresponding to that session. 
     A session manager also may generate and output an account manager user interface that identifies accounts that are associated with the user agent, and that enables the user to select the connect to, or log out of, any of various accounts to create a new session or join an active session for each account. In some embodiments, each user account will be associated with a single grant token and a single session, although other configurations may be possible.  FIG. 5  illustrates an account manager user interface  501 , in which the user can select one of multiple accounts  502   a ,  502   b  that are associated with for the user agent. Upon selection of an account, and receipt of the grant token for that account, the session manager will provide the user agent with the access token for the appropriate account. As shown, the account manager interface also displays various information about each account, such as an email address or user image for the user for the session. (As noted above, the grant token may include an address from which a user image may be returned.) 
     Optionally, one of the accounts available on the account manager user interface may be an anonymous account  503 , in which case the system may not generate a grant token at all. With an anonymous account, the user may be given limited permissions to take certain actions (such as view posts on a website, but not create or reply to those posts). 
     The two-token model can help manage multiple accounts with a single user agent. Without a two-token model, to switch accounts the user would need to actively log out of a first account, and then log into a second account by entering his or her credentials for the second account. However, if the user agent stores grant tokens for each of various accounts, the user may not be required to log in when switching to a second account. Instead, when the account manager user interface receives a request to switch from a first account to a second account, the user agent can simply retrieve the grant token for the second account and present the grant token to the web resource. 
     The two-token model also may be used to facilitate a single session across multiple web resources. For example, a user and/or a hosted service may provide a document generation service (such as a word processor) and a cloud file storage service as a common web resource, and thus may desire to treat the user&#39;s use of such services as a single session. If so, then the user&#39;s electronic device, or a different electronic device that the user is using, may include a second user agent. The second user agent may generate a second authentication request  602  to access the first web resource. The second user agent will receive access to the grant token  601 , either by the first user agent or by an endpoint that contains the grant token. The second user agent will transmit  603  the second authentication request with its credential and the grant token to a re-authentication endpoint. The re-authentication endpoint will return  604 , and the second user agent will receive, an access token in response to the second authentication request. The second user agent may use the received access token to access the web resource  605  and maintain the web session  612  until the access token expires. When the access token expires or is about to expire  606 , the second user agent may access the re-authentication endpoint and request a new access token  607  using procedures such as those discussed above in the context of  FIG. 3 . 
     As another example of how the two-token model can facilitate a single session across multiple web resources, a server provider may offer web resources in different top-level domains (TLDs) for various reasons, such as (1) offering web resources that are customized for particular countries (and this that use the TLDs for those countries); (2) to use various different brands (with the relevant brand name in the TLD), and or (3) for other purposes such as marketing purposes. The session cookie for one of these web properties may be invisible to the others, since they are in different TLDs, and because they may involve separate (and sometimes incompatible) session management systems. The two-token model may be used facilitate the integration of these web resources by issuing a common grant token that is acceptable to each of the re-authentication endpoints on the various TLDs. 
     [Similarly, a user and/or a hosted service may provide a document generation service (such as a word processor) and a cloud file storage service as a separate web resources, but still may desire to treat the user&#39;s use of such services as a single session. If so, then the first user agent may generate a second authentication request that comprises a request to access a second web resource. The first user agent may transmit the second authentication request with the grant token to the login endpoint and receive an additional access token in response to the second authentication request. The first login endpoint may use the new access token to access the second web resource and maintain the web session. In addition, this process may be used with a second user agent, in which the process of  FIG. 6  will apply, but with an access token for the second web resource instead of the first web resource. 
     In some embodiments, to maintain a session across multiple devices, a user agent of the user&#39;s first electronic may not hold a grant token, but instead the grant token may be held by a second electronic device that is in a communication range of the first electronic device. The second electronic device will include a virtual session manager that manages the session across multiple electronic device. Only client devices with a virtual session manager will holds the grant token; other client devices will not be given the grant token. In this way, dissemination of the grant token is limited to certain client devices that are have virtual session manager functionality. This will be described in more detail below. 
     The two-token model can provide several technical advantages, including better security by decreasing the time window in which access tokens must remain valid (and thus can be leaked), a better user experience by requiring the user to re-enter credentials less frequently, a standard method of terminating sessions when account security issues are detected, and operation in a multiple-device environment. 
     The multiple device environment is now described with reference back to  FIG. 1 , in which any number of client electronic devices can serve as human interface devices (HIDs) in a multiple-HID environment. Examples of client electronic devices shown include a smartphone  102 , a tablet computing device  103 , an on-board vehicle device  104 , wearable electronic devices such as a smart watch  105 , and a home voice assistant  106  or other smart home device. One or more endpoint devices  112  may be available to receive authentication requests from the client electronic devices and issue authentication tokens to the electronic devices to establish and maintain sessions across any number of hosted services  113 ,  114  via a communication network  110 . 
     In this embodiment, at least one—but not all—of the client electronic devices will include a virtual session manager. A virtual session manager is an application that stores a grant token for a session and facilitates access to the session by other client electronic devices that are not given access to the grant token.  FIG. 7  illustrates how the virtual session manager may be implemented. A first client electronic device  701  that does not include a virtual session manager may discover that a second client electronic device  702  with a virtual session manager is in a communication range of the first client electronic device  701 . The communication and transmissions between the devices may use any suitable communication protocol, such as Bluetooth, radio frequency identification, wi-fi, another short-range or near-field communication protocol, or the like. Any suitable discovery technique may be used, such as Bluetooth service delivery platform (SDP), Universal Plug and Play (UPnP), simple service discovery protocol (SSDP), or operating system-level services. If the first electronic device  701  discovers one or more devices with a virtual session manager, the user agent of the first electronic device  701  may output identifiers associated with each discovered device so that the user can select the virtual session manager to which the first electronic device  701  will connect. 
     A user agent of the second electronic device  702  may establish a web session with the web resource  705  using a process such as that described above in the context of  FIGS. 2 and 3 . In particular, when a user agent of the second electronic device  702  wishes to establish a session with a web resource  705 , it will send an authentication request to the login endpoint  714 . The authentication request is a request to access the web resource  705  and will include a credential for the user agent of the second electronic device  702 . If the credential is valid, the login endpoint  714  will return a grant token and an access token to the virtual session manager. The user agent of the second electronic device will store the grant token in the second electronic device  702  and use the access token to access the web resource  705 . When the access token has expired or is about to expire, the user agent of the second electronic device  702  may send a re-authentication request to a re-authentication endpoint  714 , which will review the request and return a new access token to the second electronic device  702  using methods such as those previously described. Any or all of the features of the grant token, access token, authentication request and re-authentication request that were described above in previous embodiments also may apply in this embodiment. 
     After another one of the client devices without a virtual session manager discovers and establishes a communication link with the second electronic device  702 , its user agent may send an authentication request to the second electronic device. For example, a user agent of the first electronic device  701  may send an authentication request to request access to the web resource by presenting a credential to the second electronic device. The authentication request may be a request to start a new session with the web resource  705 , or it may be a request to join the session that the second electronic device  702  has already established with the web resource  702 . If the request is for a new session, the virtual session manager of the second electronic device  702  will send the credential to the login endpoint  714  and receive a grant token and access token from the login endpoint  714 . If the request is to join an existing session that the user agent of the first electronic device  701  had not previously joined, or if the request is to maintain an existing session that the user agent of the first electronic device has already joined but for which the user agent&#39;s credential expired or is about to expire, the virtual session manager will send the credential and the grant token to the re-authentication endpoint  715  and obtain a new access credential for the user agent. 
     In any of these situations, after receiving the access token from the relevant endpoint, the virtual session manager will send the access token to the first electronic device  701 . The user agent of the first electronic device  701  can then save the access token and present it to the web resource  705 . The second electronic device  702  will retain the grant token for the session and will not share it with the first electronic device  701 . 
     A third electronic device  703  may also join the session with the web resource  705  using procedures matching those described above. In particular, the third electronic device  703  will send an authentication request to the second electronic device  702 . The virtual session manager of the second electronic device  702  will then send the credential and the grant token for the session to the re-authentication endpoint to obtain an access token that the user agent of the third electronic device  703  can use to access the web resource  705  and join the session. As with the second electronic device  702 , the third electronic device  703  will also not receive the grant token. 
     In any of these situations, when connecting to a virtual session manager, a user agent of a client device that does not have a virtual session manager may discover that the virtual session manager is managing multiple sessions for the first web resource. If so, then the user agent may output the identifiers for each of the virtual sessions to that the user can choose one of the virtual sessions to join, as discussed above and shown in  FIG. 5 . When the user selects one of the sessions, the user agent will transmit the selection to the virtual session manager with the authentication request, which will in turn transmit it to the applicable endpoint device with the appropriate grant token that applies to the selected session. In some embodiments, the first electronic device may allow the user to start a new session (such as anonymous session  503  in  FIG. 5 ), in which case the virtual session manager will obtain a new grant token for the new session and store the new grant token in its memory without sharing the new grant token with the first electronic device. If the user choose a new session, the virtual session manager may require the user to enter a credential into the second electronic device before it will permit the user to start a new session, and the virtual session manager may only transmit the new session request to the endpoint if it confirms that the credential authorizes the user to access the web resource (using credential verification procedures such as those described above). 
     The virtual session manager may store a history that includes one or more parameters associated with the user&#39;s use of the web resource. These parameters can include last page visited on a website, a timestamp in a video or audio stream at which a user was last presented a streaming media file, or other parameters. The parameters may be those that existed when the virtual session manager last requested an access token for the user agent by presenting a grant token to the re-authentication endpoint. When sending an access token to a client device, the virtual session manager may also send any of these parameters to the client device so that the user agent can maintain or reconnect to a virtual session in an uninterrupted manner without having to re-enter the parameters. 
     The virtual session manager may enable a smooth transition between human interface devices in a single session. In addition, multiple devices can share and participate in the same web session. An untrusted device also may be given short-term access to a session by receiving a short-lived access token, but not be given any access to a long-lived grant token. 
     The virtual session manager also may cause the second electronic device to output a user interface by which the user may manage various aspects of a session. For example, the virtual session manager may enable a user to command the virtual session manager to do any or all of the following: 
     (i) disable the virtual session, in which case the virtual session manager will disable the first access token; 
     (ii) re-enable a disabled virtual session, in which case the virtual session manager will grant an updated access token for the disabled virtual session to all electronic devices for which the virtual session manager previously disabled access; 
     (iii) re-group a virtual session, in which case the virtual session manager will identify an alternate virtual session for which it has a grant token, send the grant token for the alternate virtual session to the endpoint device, receive an alternate access token from the endpoint device, and transmit the alternate access token to the first electronic device so that the first electronic device will replace the first access token with the alternate access token and use the alternate access token to connect to the alternate virtual session; 
     (iv) disable the virtual session, in which case the virtual session manager will disable the first access token and delete the grant token for the virtual session; or 
     (v) remove the first electronic device, in which case the virtual session manager will disable the first access token and prevent the first electronic device from receiving additional access tokens until the first electronic device receives a valid authentication credential. 
     The virtual session manager also may create and store a device record for each user agent that uses the virtual session manager to join a session. The device record may include an identifier for the user agent and/or its device, session parameters for that user agent (as described above), a timestamp for when the user agent joined the session, and/or other data. In addition, the virtual session manager may cause the client device on which it runs to output a user interface by which a user may edit one or more attributes of each connected user agent, such as by giving each user agent an alias, designating the user agent as trusted or untrusted, or other attributes. 
     With any of the embodiments described above, the virtual session manager can create or serve as a virtual identity wallet for a user. The user can use the identity wallet to extend his or her identity to multiple devices on a short-term basis, and manage each device&#39;s ability to use a session, while only granting long-term access capability to a single trusted device (or a select group of trusted devices). This can give an end user more efficient control over the access privileges that he or she wishes to grant to multiple devices in a connected environment. 
     In some embodiments, the virtual session manager may expire a particular user agent&#39;s access token if the user agent experiences an action that is outside of a scope of a trusted environment. For example, if the virtual session manager cannot detect the presence of the user agent&#39;s device using discovery protocols such as those described above, this may mean that the device has exited a trusted environment such as a home or known office. If so, the virtual session manager may expire the user agent&#39;s access token until it can re-discover the user agent&#39;s device. On the other hand, when a user agent&#39;s device enters a known trusted environment, such as a home or office, it may automatically connect to the virtual session manager and join a session. The devices may know that they are in a trusted environment based on finding known GPS location data, a known wi-fi network identifier, or other suitable parameters. 
     In some embodiments, systems that employ virtual session managers may use stateful grant tokens, meaning that there will be a server-side record of each grant token issued. 
     In some embodiments, in a virtual session manger environment, the web resource or user agent may require proof demonstrating that a user is actually present when it receives an access token from a client device. If so, then the user agent may require a user presence token before it will send an access request to the web resource. If so, then the user agent may require the user to perform some user action on the client device to confirm his or her presence. The user action may be, for example, speaking a passphrase, entering a personal identification number, applying a predetermined gesture sequence to a touchscreen, or any other action that can be verified by the user agent or the virtual session manager. If the user agent or virtual session manager can confirm the user action matches an expected action, it will issue the user presence token. The user agent may include the user presence token when it transmits the access token to the web resource. 
       FIG. 8  depicts a block diagram of hardware that may be used to contain or implement program instructions, such as those of a hosted service, a monitoring service for a hosted service, an electronic device that is accessing a hosted service, or a virtual machine or container that serves in any of these roles. A bus  800  serves as an information highway interconnecting the other illustrated components of the hardware. The bus may be a physical connection between elements of the system, or a wired or wireless communication system via which various elements of the system share data. Processor  805  is a processing device of the system performing calculations and logic operations required to execute a program. Processor  805 , alone or in conjunction with one or more of the other elements disclosed in  FIG. 8 , is an example of a processing device, computing device or processor as such terms are used within this disclosure. The processing device may be a physical processing device, a virtual device contained within another processing device, or a container included within a processing device. 
     A memory device  810  is a hardware element or segment of a hardware element on which programming instructions, data, or both may be stored. Read only memory (ROM) and random access memory (RAM) constitute examples of memory devices, along with cloud storage services. 
     An optional display interface  830  may permit information to be displayed on the display  835  in audio, visual, graphic or alphanumeric format. Communication with external devices, such as a printing device, may occur using various communication devices  840 , such as a communication port or antenna. A communication device  840  may be communicatively connected to a communication network, such as the Internet or an intranet. 
     The hardware may also include a user input interface  845  which allows for receipt of data from input devices such as a keyboard or keypad  850 , or other input device  855  such as a mouse, a touchpad, a touch screen, a remote control, a pointing device, a video input device and/or a microphone. Data also may be received from an image capturing device  820  such as a digital camera or video camera. A positional sensor  860  and/or motion sensor  870  may be included to detect position and movement of the device. Examples of motion sensors  870  include gyroscopes or accelerometers. Examples of positional sensors  860  such as a global positioning system (GPS) sensor device that receives positional data from an external GPS network. 
     The features and functions described above, as well as alternatives, may be combined into many other different systems or applications. Various alternatives, modifications, variations or improvements may be made by those skilled in the art, each of which is also intended to be encompassed by the disclosed embodiments.