From 07fa53ec40106b97ba2c12a2dcc5446325e5fb61 Mon Sep 17 00:00:00 2001
From: reivilibre <oliverw@matrix.org>
Date: Thu, 5 May 2022 13:39:59 +0100
Subject: [PATCH] Improve comments and error messages around access tokens.
 (#12577)

---
 changelog.d/12577.misc |  1 +
 synapse/api/auth.py    | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 8 deletions(-)
 create mode 100644 changelog.d/12577.misc

diff --git a/changelog.d/12577.misc b/changelog.d/12577.misc
new file mode 100644
index 000000000..8c4c47ad5
--- /dev/null
+++ b/changelog.d/12577.misc
@@ -0,0 +1 @@
+Improve comments and error messages around access tokens.
\ No newline at end of file
diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index f6202ef7a..931750668 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -417,7 +417,8 @@ class Auth:
         """
 
         if rights == "access":
-            # first look in the database
+            # First look in the database to see if the access token is present
+            # as an opaque token.
             r = await self.store.get_user_by_access_token(token)
             if r:
                 valid_until_ms = r.valid_until_ms
@@ -434,7 +435,8 @@ class Auth:
 
                 return r
 
-        # otherwise it needs to be a valid macaroon
+        # If the token isn't found in the database, then it could still be a
+        # macaroon, so we check that here.
         try:
             user_id, guest = self._parse_and_validate_macaroon(token, rights)
 
@@ -482,8 +484,12 @@ class Auth:
             TypeError,
             ValueError,
         ) as e:
-            logger.warning("Invalid macaroon in auth: %s %s", type(e), e)
-            raise InvalidClientTokenError("Invalid macaroon passed.")
+            logger.warning(
+                "Invalid access token in auth: %s %s.",
+                type(e),
+                e,
+            )
+            raise InvalidClientTokenError("Invalid access token passed.")
 
     def _parse_and_validate_macaroon(
         self, token: str, rights: str = "access"
@@ -504,10 +510,7 @@ class Auth:
         try:
             macaroon = pymacaroons.Macaroon.deserialize(token)
         except Exception:  # deserialize can throw more-or-less anything
-            # doesn't look like a macaroon: treat it as an opaque token which
-            # must be in the database.
-            # TODO: it would be nice to get rid of this, but apparently some
-            # people use access tokens which aren't macaroons
+            # The access token doesn't look like a macaroon.
             raise _InvalidMacaroonException()
 
         try: