Redo OIDC configuration (#2020)

expand user, add claims to user

This commit expands the user table with additional fields that
can be retrieved from OIDC providers (and other places) and
uses this data in various tailscale response objects if it is
available.

This is the beginning of implementing
https://docs.google.com/document/d/1X85PMxIaVWDF6T_UPji3OeeUqVBcGj_uHRM5CI-AwlY/edit
trying to make OIDC more coherant and maintainable in addition
to giving the user a better experience and integration with a
provider.

remove usernames in magic dns, normalisation of emails

this commit removes the option to have usernames as part of MagicDNS
domains and headscale will now align with Tailscale, where there is a
root domain, and the machine name.

In addition, the various normalisation functions for dns names has been
made lighter not caring about username and special character that wont
occur.

Email are no longer normalised as part of the policy processing.

untagle oidc and regcache, use typed cache

This commits stops reusing the registration cache for oidc
purposes and switches the cache to be types and not use any
allowing the removal of a bunch of casting.

try to make reauth/register branches clearer in oidc

Currently there was a function that did a bunch of stuff,
finding the machine key, trying to find the node, reauthing
the node, returning some status, and it was called validate
which was very confusing.

This commit tries to split this into what to do if the node
exists, if it needs to register etc.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

CHANGELOG.md

@@ -2,11 +2,25 @@
 
 ## Next
 
+### BREAKING
+
+- Remove `dns.use_username_in_magic_dns` configuration option [#2020](https://github.com/juanfont/headscale/pull/2020)
+  - Having usernames in magic DNS is no longer possible.
+- Redo OpenID Connect configuration [#2020](https://github.com/juanfont/headscale/pull/2020)
+  - `strip_email_domain` has been removed, domain is _always_ part of the username for OIDC.
+  - Users are now identified by `sub` claim in the ID token instead of username, allowing the username, name and email to be updated.
+  - User has been extended to store username, display name, profile picture url and email.
+    - These fields are forwarded to the client, and shows up nicely in the user switcher.
+    - These fields can be made available via the API/CLI for non-OIDC users in the future.
 - Remove versions older than 1.56 [#2149](https://github.com/juanfont/headscale/pull/2149)
   - Clean up old code required by old versions
+
+### Changes
+
 - Improved compatibilty of built-in DERP server with clients connecting over WebSocket.
 - Allow nodes to use SSH agent forwarding [#2145](https://github.com/juanfont/headscale/pull/2145)
 
+
 ## 0.23.0 (2024-09-18)
 
 This release was intended to be mainly a code reorganisation and refactoring, significantly improving the maintainability of the codebase. This should allow us to improve further and make it easier for the maintainers to keep on top of the project.