Fix check_auth to return None on failure, not False

[reivilibre]

See https://matrix-org.github.io/synapse/latest/password_auth_providers.html#optional-methods

Also note that the source code of Synapse suggests the return value of False triggers an error.

[clokep]

Also note that the source code of Synapse suggests the return value of False triggers an error.

I'm having trouble unwrapping the many layers of code we have for these. I would have thought synapse just checks if the result is truth-y and that's why it used to work. Can you link to where an error in Synapse would happen?

[reivilibre]

I'm having trouble unwrapping the many layers of code we have for these

I have to say I do relate to this statement. I've never seen a more confusing module system, though maybe I'm just too used to seeing this kind of thing in Java. 😖

Related lines:

• https://github.com/matrix-org/synapse/blob/e5cdb9e2339e321e8a77a898d362d7fbc476303b/synapse/handlers/auth.py#L2034 (key)
• https://github.com/matrix-org/synapse/blob/e5cdb9e2339e321e8a77a898d362d7fbc476303b/synapse/handlers/auth.py#L2171 (site where the error triggers: if the return value is not None and it's not a tuple, an error is generated)

Out of interest, check_3pid_auth has the same set-up, but the LDAP3 module is set up properly.

[clokep]

Thanks! I think the change looks fine, could be interesting to know if this ever worked or not, but...probably not worth delving too deep into the history.