fix: extend forgejo_auth_token table

- Add a `purpose` column, this allows the `forgejo_auth_token` table to
be used by other parts of Forgejo, while still enjoying the
no-compromise architecture.
- Remove the 'roll your own crypto' time limited code functions and
migrate them to the `forgejo_auth_token` table. This migration ensures
generated codes can only be used for their purpose and ensure they are
invalidated after their usage by deleting it from the database, this
also should help making auditing of the security code easier, as we're
no longer trying to stuff a lot of data into a HMAC construction.
-Helper functions are rewritten to ensure a safe-by-design approach to
these tokens.
- Add the `forgejo_auth_token` to dbconsistency doctor and add it to the
`deleteUser` function.
- TODO: Add cron job to delete expired authorization tokens.
- Unit and integration tests added.

services/doctor/dbconsistency.go

@@ -243,6 +243,9 @@ func checkDBConsistency(ctx context.Context, logger log.Logger, autofix bool) er
 		// find archive download count without existing release
 		genericOrphanCheck("Archive download count without existing Release",
 			"repo_archive_download_count", "release", "repo_archive_download_count.release_id=release.id"),
+		// find authorization tokens without existing user
+		genericOrphanCheck("Authorization token without existing User",
+			"forgejo_auth_token", "user", "forgejo_auth_token.uid=user.id"),
 	)
 
 	for _, c := range consistencyChecks {