Allow users to register with a registration token without requiring registration_requires_token to be enabled

[Half-Shot]

Currently, the flow for m.login.registration_token is only valid when the config flag registration_requires_token is enabled. This means even if you have valid registration tokens available in Synapse, they won't work unless they are required by the config. This poses a problem for our system as we use these registration tokens with a Synapse module to perform special actions if the user has registered via a token.

It seems fairly harmless to allow these tokens to be used, regardless of Synapse configuration, if the admin has registered these tokens. At the very least it would be nice to differentiate between "required" and "disabled".

[H-Shay]

Just to clarify, what you'd like to see is an option for token registration to be enabled but not required, correct?

[Half-Shot]

Yep, exactly that.

[squahtx]

related: #12526 Add option to enable token registration without requiring 3pids,
which added a config flag that creates a registration token flow as an alternative to required 3pids.