Rules for what usernames are supported

[phil-davis]

It seems that usernames starting with a digit are not supported by default.
See discussion in owncloud/ocis#6194

But they do work if this setting is used:
GRAPH_USERNAME_MATCH=none

I also came across this in PR owncloud/ocis#6279 which adds some test examples of usernames that start with a digit.

Should we document this somewhere?

Are there other GRAPH_*settings that are also useful to mention in docs?

Or are these things part of a "standard" GraphAPI and documentation should just have a link to somewhere where all the GraphAPI settings are described?

[mmattel]

Added a note to the referenced issue (6194) that we need to clarify the description text before we highlight the problem/solution.

Are there other GRAPH_*settings that are also useful to mention in docs

I strongly believe so 🤣

[mmattel]

Referencing: owncloud/ocis#6381 (Add a note in the graph readme to tell that one can restrict usernames)