Add Tailscale custom OIDC webfinger

See: https://tailscale.com/kb/1240/sso-custom-oidc/#webfinger-setup

hosts/flora-6/caddy.nix

@@ -32,6 +32,21 @@
                       redir https://mastodon.pub.solar{uri}
                     }
 
+                    # Tailscale OIDC requirement
+                    handle /.well-known/webfinger {
+                      respond 200 {
+                        body `{
+            "subject": "acct:admins@pub.solar",
+            "links": [
+              {
+                "rel": "http://openid.net/specs/connect/1.0/issuer",
+                "href": "https://auth.pub.solar/realms/pub.solar"
+              }
+            ]
+          }`
+                      }
+                    }
+
                     # redirect to statutes
                     redir /satzung https://cloud.pub.solar/s/2tRCP9aZFCiWxQy temporary