Domains are case sensitive

[pulecp]

Hello dear developers,

Describe the problem
I use Azure as a provider but I suppose that this issue affects all providers. The following log line should be self-explaining.

{"level":"warn","ts":xxx,"msg":"domain Example.com not found in any domains [example.com]"}

The domain comparison (I guess in this part of code for example) is case sensitive and does not allow to use just one variation like:

vouch:
  domains:
    - example.com

but I would have to use all cases like:

vouch:
  domains:
    - example.com
    - Example.com
    - exAMPle.com
    - ...

to match RFC1035 saying that domains are case in-sensitive.

Expected behavior

All domains (also for whitelisting of users) are case in-sensitive.

Thanks for taking this into consideration.

[bnfinet]

@pulecp yep, you're right, that's how it should work

All domains should be string.toLower()'d before comparison. Need to make sure that doesn't screw up unicode domains in any way. Perhaps there's a comparison library that should be used but I haven't gone searching for one.

issue #324 and PR #325 are similar and relevant