MSC2918 Refresh tokens implementation (#9450)

This implements refresh tokens, as defined by MSC2918

This MSC has been implemented client side in Hydrogen Web: vector-im/hydrogen-web#235

The basics of the MSC works: requesting refresh tokens on login, having the access tokens expire, and using the refresh token to get a new one.

Signed-off-by: Quentin Gliech <quentingliech@gmail.com>

synapse/handlers/auth.py

@@ -30,6 +30,7 @@ from typing import (
     Optional,
     Tuple,
     Union,
+    cast,
 )
 
 import attr
@@ -72,6 +73,7 @@ from synapse.util.stringutils import base62_encode
 from synapse.util.threepids import canonicalise_email
 
 if TYPE_CHECKING:
+    from synapse.rest.client.v1.login import LoginResponse
     from synapse.server import HomeServer
 
 logger = logging.getLogger(__name__)
@@ -777,6 +779,108 @@ class AuthHandler(BaseHandler):
             "params": params,
         }
 
+    async def refresh_token(
+        self,
+        refresh_token: str,
+        valid_until_ms: Optional[int],
+    ) -> Tuple[str, str]:
+        """
+        Consumes a refresh token and generate both a new access token and a new refresh token from it.
+
+        The consumed refresh token is considered invalid after the first use of the new access token or the new refresh token.
+
+        Args:
+            refresh_token: The token to consume.
+            valid_until_ms: The expiration timestamp of the new access token.
+
+        Returns:
+            A tuple containing the new access token and refresh token
+        """
+
+        # Verify the token signature first before looking up the token
+        if not self._verify_refresh_token(refresh_token):
+            raise SynapseError(401, "invalid refresh token", Codes.UNKNOWN_TOKEN)
+
+        existing_token = await self.store.lookup_refresh_token(refresh_token)
+        if existing_token is None:
+            raise SynapseError(401, "refresh token does not exist", Codes.UNKNOWN_TOKEN)
+
+        if (
+            existing_token.has_next_access_token_been_used
+            or existing_token.has_next_refresh_token_been_refreshed
+        ):
+            raise SynapseError(
+                403, "refresh token isn't valid anymore", Codes.FORBIDDEN
+            )
+
+        (
+            new_refresh_token,
+            new_refresh_token_id,
+        ) = await self.get_refresh_token_for_user_id(
+            user_id=existing_token.user_id, device_id=existing_token.device_id
+        )
+        access_token = await self.get_access_token_for_user_id(
+            user_id=existing_token.user_id,
+            device_id=existing_token.device_id,
+            valid_until_ms=valid_until_ms,
+            refresh_token_id=new_refresh_token_id,
+        )
+        await self.store.replace_refresh_token(
+            existing_token.token_id, new_refresh_token_id
+        )
+        return access_token, new_refresh_token
+
+    def _verify_refresh_token(self, token: str) -> bool:
+        """
+        Verifies the shape of a refresh token.
+
+        Args:
+            token: The refresh token to verify
+
+        Returns:
+            Whether the token has the right shape
+        """
+        parts = token.split("_", maxsplit=4)
+        if len(parts) != 4:
+            return False
+
+        type, localpart, rand, crc = parts
+
+        # Refresh tokens are prefixed by "syr_", let's check that
+        if type != "syr":
+            return False
+
+        # Check the CRC
+        base = f"{type}_{localpart}_{rand}"
+        expected_crc = base62_encode(crc32(base.encode("ascii")), minwidth=6)
+        if crc != expected_crc:
+            return False
+
+        return True
+
+    async def get_refresh_token_for_user_id(
+        self,
+        user_id: str,
+        device_id: str,
+    ) -> Tuple[str, int]:
+        """
+        Creates a new refresh token for the user with the given user ID.
+
+        Args:
+            user_id: canonical user ID
+            device_id: the device ID to associate with the token.
+
+        Returns:
+            The newly created refresh token and its ID in the database
+        """
+        refresh_token = self.generate_refresh_token(UserID.from_string(user_id))
+        refresh_token_id = await self.store.add_refresh_token_to_user(
+            user_id=user_id,
+            token=refresh_token,
+            device_id=device_id,
+        )
+        return refresh_token, refresh_token_id
+
     async def get_access_token_for_user_id(
         self,
         user_id: str,
@@ -784,6 +888,7 @@ class AuthHandler(BaseHandler):
         valid_until_ms: Optional[int],
         puppets_user_id: Optional[str] = None,
         is_appservice_ghost: bool = False,
+        refresh_token_id: Optional[int] = None,
     ) -> str:
         """
         Creates a new access token for the user with the given user ID.
@@ -801,6 +906,8 @@ class AuthHandler(BaseHandler):
             valid_until_ms: when the token is valid until. None for
                 no expiry.
             is_appservice_ghost: Whether the user is an application ghost user
+            refresh_token_id: the refresh token ID that will be associated with
+                this access token.
         Returns:
               The access token for the user's session.
         Raises:
@@ -836,6 +943,7 @@ class AuthHandler(BaseHandler):
             device_id=device_id,
             valid_until_ms=valid_until_ms,
             puppets_user_id=puppets_user_id,
+            refresh_token_id=refresh_token_id,
         )
 
         # the device *should* have been registered before we got here; however,
@@ -928,7 +1036,7 @@ class AuthHandler(BaseHandler):
         self,
         login_submission: Dict[str, Any],
         ratelimit: bool = False,
-    ) -> Tuple[str, Optional[Callable[[Dict[str, str]], Awaitable[None]]]]:
+    ) -> Tuple[str, Optional[Callable[["LoginResponse"], Awaitable[None]]]]:
         """Authenticates the user for the /login API
 
         Also used by the user-interactive auth flow to validate auth types which don't
@@ -1073,7 +1181,7 @@ class AuthHandler(BaseHandler):
         self,
         username: str,
         login_submission: Dict[str, Any],
-    ) -> Tuple[str, Optional[Callable[[Dict[str, str]], Awaitable[None]]]]:
+    ) -> Tuple[str, Optional[Callable[["LoginResponse"], Awaitable[None]]]]:
         """Helper for validate_login
 
         Handles login, once we've mapped 3pids onto userids
@@ -1151,7 +1259,7 @@ class AuthHandler(BaseHandler):
 
     async def check_password_provider_3pid(
         self, medium: str, address: str, password: str
-    ) -> Tuple[Optional[str], Optional[Callable[[Dict[str, str]], Awaitable[None]]]]:
+    ) -> Tuple[Optional[str], Optional[Callable[["LoginResponse"], Awaitable[None]]]]:
         """Check if a password provider is able to validate a thirdparty login
 
         Args:
@@ -1215,6 +1323,19 @@ class AuthHandler(BaseHandler):
         crc = base62_encode(crc32(base.encode("ascii")), minwidth=6)
         return f"{base}_{crc}"
 
+    def generate_refresh_token(self, for_user: UserID) -> str:
+        """Generates an opaque string, for use as a refresh token"""
+
+        # we use the following format for refresh tokens:
+        #    syr_<base64 local part>_<random string>_<base62 crc check>
+
+        b64local = unpaddedbase64.encode_base64(for_user.localpart.encode("utf-8"))
+        random_string = stringutils.random_string(20)
+        base = f"syr_{b64local}_{random_string}"
+
+        crc = base62_encode(crc32(base.encode("ascii")), minwidth=6)
+        return f"{base}_{crc}"
+
     async def validate_short_term_login_token(
         self, login_token: str
     ) -> LoginTokenAttributes:
@@ -1563,7 +1684,7 @@ class AuthHandler(BaseHandler):
         )
         respond_with_html(request, 200, html)
 
-    async def _sso_login_callback(self, login_result: JsonDict) -> None:
+    async def _sso_login_callback(self, login_result: "LoginResponse") -> None:
         """
         A login callback which might add additional attributes to the login response.
 
@@ -1577,7 +1698,8 @@ class AuthHandler(BaseHandler):
 
         extra_attributes = self._extra_attributes.get(login_result["user_id"])
         if extra_attributes:
-            login_result.update(extra_attributes.extra_attributes)
+            login_result_dict = cast(Dict[str, Any], login_result)
+            login_result_dict.update(extra_attributes.extra_attributes)
 
     def _expire_sso_extra_attributes(self) -> None:
         """