Why does upstream OAuth registration limit username to 14 characters?

[eforest]

Why does upstream OAuth registration limit username to 14 characters?
Is there any reason regarding integration with matrix-home-server?

see https://github.com/matrix-org/matrix-authentication-service/blob/main/policies/register.rego [21-23]

Best Regards

[sandhose]

I think this is a leftover from when I implemented the policy engine. There are no good reason for this arbitrary limit

[sandhose]

#2471 bumped the limit to 64 characters. It's still a somewhat arbitrary limit, but probably better than before. I need to investigate what would be the impact of a very very long MXID

[thegcat]

Quick heads-up here as we ran into the other side of the problem (a user with a 2-character username getting bumped by MAS, issue incoming): the spec only limits the total length of the MXID to 255 characters, so the upper bound for a username would be 255 - length of the server name - 2.