Project: Teleport (Provisioning / Security & Compliance)
File: 0093-offline-access.md

authors: Tim Ross (tim.ross@goteleport.com) state: draft Engineering @zmb3 && (fspmarshall || codingllama) Ensure that users can access nodes via `tsh ssh` when there is intermittent or no connectivity to Auth. Connectivity to the Auth server is a single point of failure which can result in not being able to access a resource. If a user already has already obtained a valid certificate (via `tsh login`) there are certain scenarios when a connection to Auth should not required to gain access to a node. This would reduce the burden on cluster admins when performing an Auth upgrade. On top of the potential downtime during the upgrade, any issues found as a result of the upgrade require a rollback, which can further extend downtime and lack of connectivity. The following cluster settings or operations must have a connection to Auth server to establish a connection to a node: ```bash tsh ssh user@"foo=bar" ``` For the above command to work, `tsh` needs to be able to resolve all matching nodes which have the label `foo=bar`. To determine which nodes match the provided labels `tsh` issues a `proto.AuthService/ListResources` request to the Auth server which returns the matching node set. Without a connection to Auth node resolution is just not possible. Both `proxy-sync` and `node-sync` recording modes require a persistent connection to Auth to upload session recordings. As a result, even if `tsh ssh` doesn't require a connection to Auth, the session cannot be created without being able to start a connection for the recordings. This will prevent the connection to the node from being established successfully. When enabled at either the cluster or role level per-session MFA requires completing the MFA ceremony with the Auth server. This means that it is not possible to connect to a resource without `tsh` being able to connect to the Auth server to perform the required MFA ceremony. Future Improvements There is a scenario in the future that would allow for such behavior to exist. Per , setting `requiresessionmfa` to `hardwarekeytouch` does not require the Auth server for the MFA ceremony. Instead the PIV stored keys only require a PIV-touch to satisfy the per-session MFA requirement. Tracking participants for a moderated session requires persisting the `types.SessionTracker` resource in the backend so that the joining criteria may be evaluated when a user creates or joins a session. In the event that persisting the `types.SessionTracker` fails, the session must be aborted to prevent any unauthorized access. This is true for both proxy and node recording mode. All access via the Web UI requires a connection to Auth. None of the auth connector resources are replicated to the Proxy which means users are unable to login to the Web UI without connectivity to

Even when already logged in prior to losing connection to Auth, the Proxy doesn't perform any RBAC for users locally. It instead relies on proxying all requests to the Auth server on behalf of the logged in user for RBAC to be performed. ```yaml kind: role version: v5 metadata: name: lock-strict spec: options: lock: strict ``` Strict mode, which is not the default mode, causes all interactions to be terminated when the locks are not guaranteed to be up to date. When connectivity to Auth is interrupted and locks aren't able to be replicated, new connections will eventually be aborted out of an abundance of caution. Attempting to connect directly to a node via hostname, IP Address, or UUID should not require a connection to Auth for any configurations except those mentioned above. ```bash tsh ssh foo@bar tsh ssh foo@127.0.0.1 tsh ssh foo@f409a8b6-1275-4f0f-887e-8185426147f4 ``` However, this doesn't work to date for two main reasons: 1) `proto.AuthService/IsMFARequired` 2) `types.SessionTracker` `tsh` determines whether per-session MFA is required prior to connecting to a node. Which means that every invocation of `tsh ssh` requires a connection to the Auth server. Successful connection attempt when Auth is available: ```mermaid sequenceDiagram participant tsh participant Auth participant Node tsh->>+Auth: IsMFARequired Auth-->>-tsh: yes tsh->>+Auth: perform mfa ceremony Auth-->>+tsh: issue challenge tsh-->>+Auth: challenge response Auth-->>+tsh: issue certificates tsh->>+Node: Connect Node-->>+tsh: Success ``` Failed connection attempt when Auth is unavailable: ```mermaid sequenceDiagram participant tsh participant Auth participant Node tsh->>+Auth: IsMFARequired Auth-->>-tsh: Error ``` However, the decision if the connection should be established is ultimately made by the node, not the Auth server. The node performs an RBAC check on all inbound connections to determine if among other things per-session MFA is required and the MFA ceremony was performed. Thus, `tsh` should always attempt to connect to a node first, and only try `proto.AuthService/IsMFARequired` if the node response with a `trace.AccessDenied` error. If per session MFA is required, then `tsh` should perform the MFA ceremony and attempt to connect to the node again, otherwise the original `trace.AccessDenied` error should be returned as the user doesn't have access to the node due to their role. In the happy path, this reduces latency to connect to nodes and increase the availability of the node by removing the Auth server from the connection path. When per session MFA is required this increases latency by a connection attempt to the Node. Successful connection attempt when Auth isn't available and per-session MFA is not required ```mermaid sequenceDiagram participant tsh participant Auth participant Node tsh->>+Node: Connect Node-->>+tsh: Success ``` Failed connection attempt when Auth is unavailable and per-session MFA is required: ```mermaid sequenceDiagram participant tsh participant Auth participant Node tsh->>+Node: Connect Node-->>+tsh: Access Denied tsh->>+Auth: IsMFARequired Auth-->>-tsh: Error ``` Alternative approaches: 1) First try

and always try to connect to the Node regardless of error determining if per session MFA is required Results in increased latency for the happy path which doesn't require per-session MFA by requiring the call to `proto.AuthService/IsMFARequired`. However, `proto.AuthService/IsMFARequired` is still required if the user doesn't have access to the node at all or per-session MFA is required. Results in decreased latency when per-session MFA is required since that flow now requires establishing the connection to the target node once. 2) Perform `proto.AuthService/IsMFARequired` and connecting to the node in parallel and act accordingly Ultimately leads to roughly the same outcome as the recommended option. The connection to the node almost always takes longer than the connection to auth. By performing them in parallel you really only get gains in the happy path. A new session tracker is created for every session. In the event that persisting the session tracker fails the session is aborted. Instead of immediately aborting the session if the session tracker cannot be persisted, the node could first check if moderated sessions are required. In the event that they aren't the session should be allowed to proceed using a local session tracker resource. While this does allow access to the node, it will prevent the following: the session from appearing in the active sessions list the session will not be joinable by other users the session recording will not be available until the UploadCompleter processes it Connect leverages `tsh` for its backend operations, which means that while it suffers from the same issues that `tsh ssh` does today, it will also benefit from the proposals laid out in this RFD. That is, there shouldn't be any Connect specific code that needs to change in order for offline access to nodes to work in Connect. All versions of Connect that bundle a version of `tsh` which includes the changes proposed in this RFD should automatically gain access to nodes without access to Auth (permitted all the required cluster configurations are met of course). Tests will be added to verify that in each scenario described in this RFD that access to the node is as expected. The changes to `tsh` should not impact security at all. They will still enforce that per-session MFA is performed if required. Nodes ultimately make the decision if access should be allowed and the changes proposed are client side only. Allowing non-moderated sessions to continue without the session tracker in the backend means does pose some auditing risk. There should be no perceivable change to the UX of `tsh ssh` for a healthy cluster. When there is an Auth outage access to nodes should be permitted in the allowed configurations listed above. The changes here do result in a slightly longer failure scenario when there is an Auth outage and per-session MFA is required for `tsh ssh`, however the total time will be no longer than it would've take to establish the connection to the node if Auth was available.