A method for authenticating an application, the method comprising: receiving, at a server, a first authorization request from a client device originating from a first authorization module of a first application executing on the client device, wherein the first application is configured to launch the first authorization module or to provide control to the first authorization module to cause transmission of the first authorization request, wherein the first authorization module is configured to obtain an identifier identifying the client device, wherein the first authorization request comprises the identifier; causing, in response to the first authorization request and using the identifier, transmission of a verification message to the client device, wherein the verification message comprises a verification code; receiving, at the server, a confirmation of the verification code from the first authorization module of the first application executing on the client device; authenticating, at the server, the first application, wherein receiving the confirmation of the verification code confirms that the first authorization module making the authorization request is included in the client device identified by the identifier; determining, after authenticating the first application, that the client device identified by the identifier corresponds to a user account that includes secure user data associated with a user; and after authenticating the first application, transmitting, to the first authorization module of the first application, a first unique token verifying that the first application is authorized to sign into the user account, wherein use of the first unique token allows the first application to sign into the user account, wherein: the first unique token uniquely identifies the user account to the first application, and the first application is, using the first unique token, permitted to sign into the user account but not permitted to access the secure user data. receiving, at a server, a first authorization request from a client device originating from a first authorization module of a first application executing on the client device, wherein the first application is configured to launch the first authorization module or to provide control to the first authorization module to cause transmission of the first authorization request, wherein the first authorization module is configured to obtain an identifier identifying the client device, wherein the first authorization request comprises the identifier; causing, in response to the first authorization request and using the identifier, transmission of a verification message to the client device, wherein the verification message comprises a verification code; receiving, at the server, a confirmation of the verification code from the first authorization module of the first application executing on the client device; authenticating, at the server, the first application, wherein receiving the confirmation of the verification code confirms that the first authorization module making the authorization request is included in the client device identified by the identifier; determining, after authenticating the first application, that the client device identified by the identifier corresponds to a user account that includes secure user data associated with a user; and after authenticating the first application, transmitting, to the first authorization module of the first application, a first unique token verifying that the first application is authorized to sign into the user account, wherein use of the first unique token allows the first application to sign into the user account, wherein: the first unique token uniquely identifies the user account to the first application, and the first application is, using the first unique token, permitted to sign into the user account but not permitted to access the secure user data. the first unique token uniquely identifies the user account to the first application, and the first application is, using the first unique token, permitted to sign into the user account but not permitted to access the secure user data.