Secure permissioning of access to user accounts, including secure deauthorization of access to user accounts

A computer-implemented method of providing user account data, the computer-implemented method comprising: by one or more hardware processors executing program instructions: receiving a cryptographic token associated with an authorization request initiated via a first computing device, wherein the cryptographic token is further associated with an institution and a user account held by the institution; receiving a request for user account data from a second computing device, wherein the second computing device is associated with an external application; providing, to a computing device associated with the institution: the cryptographic token, and a request for user account data associated with the user account; receiving user account data from the computing device associated with the institution; and providing the user account data to at least one of: the second computing device, or a computing device associated with a trusted third-party transaction processor.