Some identity providers (auth0 for example) do not allow to set the
groups claims and administrators must use custom claims names and add
them in the id token.
This commit adds the following configuration options:
- `oidc.groups_claim` to set the groups claim name
- `oidc.email_claim` to set the email claim name
All claims default to the previous values for backwards compatibility.
The groups claim can now also accept `[]string` or `string` as some
providers might return only a string response instead of array.
There was a lot of tests that actually threw a lot of errors and that did
not pass all the way because we didnt check everything. This commit should
fix all of these cases.
Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>
