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Reject unknown UI auth sessions (instead of silently generating a new one) (#7268)
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Patrick Cloke
GitHub
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changelog.d/7268.bugfix
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1
changelog.d/7268.bugfix
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@ -0,0 +1 @@
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Reject unknown session IDs during user interactive authentication instead of silently creating a new session.
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@ -257,10 +257,6 @@ class AuthHandler(BaseHandler):
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Takes a dictionary sent by the client in the login / registration
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protocol and handles the User-Interactive Auth flow.
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As a side effect, this function fills in the 'creds' key on the user's
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session with a map, which maps each auth-type (str) to the relevant
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identity authenticated by that auth-type (mostly str, but for captcha, bool).
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If no auth flows have been completed successfully, raises an
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InteractiveAuthIncompleteError. To handle this, you can use
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synapse.rest.client.v2_alpha._base.interactive_auth_handler as a
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@ -304,50 +300,47 @@ class AuthHandler(BaseHandler):
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del clientdict["auth"]
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if "session" in authdict:
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sid = authdict["session"]
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session = self._get_session_info(sid)
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if len(clientdict) > 0:
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# This was designed to allow the client to omit the parameters
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# and just supply the session in subsequent calls so it split
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# auth between devices by just sharing the session, (eg. so you
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# could continue registration from your phone having clicked the
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# email auth link on there). It's probably too open to abuse
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# because it lets unauthenticated clients store arbitrary objects
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# on a homeserver.
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# Revisit: Assuming the REST APIs do sensible validation, the data
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# isn't arbintrary.
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session["clientdict"] = clientdict
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self._save_session(session)
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elif "clientdict" in session:
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clientdict = session["clientdict"]
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# Ensure that the queried operation does not vary between stages of
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# the UI authentication session. This is done by generating a stable
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# comparator based on the URI, method, and body (minus the auth dict)
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# and storing it during the initial query. Subsequent queries ensure
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# that this comparator has not changed.
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comparator = (request.uri, request.method, clientdict)
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if "ui_auth" not in session:
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session["ui_auth"] = comparator
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self._save_session(session)
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elif session["ui_auth"] != comparator:
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raise SynapseError(
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403,
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"Requested operation has changed during the UI authentication session.",
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# If there's no session ID, create a new session.
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if not sid:
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session = self._create_session(
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clientdict, (request.uri, request.method, clientdict), description
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)
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session_id = session["id"]
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# Add a human readable description to the session.
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if "description" not in session:
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session["description"] = description
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self._save_session(session)
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else:
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session = self._get_session_info(sid)
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session_id = sid
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if not clientdict:
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# This was designed to allow the client to omit the parameters
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# and just supply the session in subsequent calls so it split
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# auth between devices by just sharing the session, (eg. so you
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# could continue registration from your phone having clicked the
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# email auth link on there). It's probably too open to abuse
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# because it lets unauthenticated clients store arbitrary objects
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# on a homeserver.
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# Revisit: Assuming the REST APIs do sensible validation, the data
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# isn't arbitrary.
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clientdict = session["clientdict"]
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# Ensure that the queried operation does not vary between stages of
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# the UI authentication session. This is done by generating a stable
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# comparator based on the URI, method, and body (minus the auth dict)
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# and storing it during the initial query. Subsequent queries ensure
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# that this comparator has not changed.
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comparator = (request.uri, request.method, clientdict)
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if session["ui_auth"] != comparator:
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raise SynapseError(
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403,
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"Requested operation has changed during the UI authentication session.",
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)
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if not authdict:
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raise InteractiveAuthIncompleteError(
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self._auth_dict_for_flows(flows, session)
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self._auth_dict_for_flows(flows, session_id)
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)
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if "creds" not in session:
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session["creds"] = {}
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creds = session["creds"]
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# check auth type currently being presented
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@ -387,9 +380,9 @@ class AuthHandler(BaseHandler):
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list(clientdict),
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)
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return creds, clientdict, session["id"]
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return creds, clientdict, session_id
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ret = self._auth_dict_for_flows(flows, session)
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ret = self._auth_dict_for_flows(flows, session_id)
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ret["completed"] = list(creds)
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ret.update(errordict)
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raise InteractiveAuthIncompleteError(ret)
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@ -407,8 +400,6 @@ class AuthHandler(BaseHandler):
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raise LoginError(400, "", Codes.MISSING_PARAM)
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sess = self._get_session_info(authdict["session"])
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if "creds" not in sess:
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sess["creds"] = {}
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creds = sess["creds"]
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result = await self.checkers[stagetype].check_auth(authdict, clientip)
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@ -448,7 +439,7 @@ class AuthHandler(BaseHandler):
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value: The data to store
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"""
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sess = self._get_session_info(session_id)
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sess.setdefault("serverdict", {})[key] = value
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sess["serverdict"][key] = value
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self._save_session(sess)
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def get_session_data(
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@ -463,7 +454,7 @@ class AuthHandler(BaseHandler):
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default: Value to return if the key has not been set
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"""
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sess = self._get_session_info(session_id)
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return sess.setdefault("serverdict", {}).get(key, default)
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return sess["serverdict"].get(key, default)
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async def _check_auth_dict(
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self, authdict: Dict[str, Any], clientip: str
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@ -519,7 +510,7 @@ class AuthHandler(BaseHandler):
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}
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def _auth_dict_for_flows(
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self, flows: List[List[str]], session: Dict[str, Any]
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self, flows: List[List[str]], session_id: str,
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) -> Dict[str, Any]:
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public_flows = []
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for f in flows:
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@ -538,28 +529,71 @@ class AuthHandler(BaseHandler):
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params[stage] = get_params[stage]()
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return {
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"session": session["id"],
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"session": session_id,
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"flows": [{"stages": f} for f in public_flows],
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"params": params,
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}
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def _get_session_info(self, session_id: Optional[str]) -> dict:
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def _create_session(
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self,
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clientdict: Dict[str, Any],
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ui_auth: Tuple[bytes, bytes, Dict[str, Any]],
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description: str,
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) -> dict:
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"""
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Gets or creates a session given a session ID.
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Creates a new user interactive authentication session.
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The session can be used to track data across multiple requests, e.g. for
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interactive authentication.
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Each session has the following keys:
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id:
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A unique identifier for this session. Passed back to the client
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and returned for each stage.
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clientdict:
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The dictionary from the client root level, not the 'auth' key.
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ui_auth:
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A tuple which is checked at each stage of the authentication to
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ensure that the asked for operation has not changed.
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creds:
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A map, which maps each auth-type (str) to the relevant identity
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authenticated by that auth-type (mostly str, but for captcha, bool).
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serverdict:
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A map of data that is stored server-side and cannot be modified
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by the client.
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description:
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A string description of the operation that the current
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authentication is authorising.
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Returns:
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The newly created session.
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"""
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session_id = None
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while session_id is None or session_id in self.sessions:
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session_id = stringutils.random_string(24)
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self.sessions[session_id] = {
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"id": session_id,
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"clientdict": clientdict,
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"ui_auth": ui_auth,
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"creds": {},
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"serverdict": {},
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"description": description,
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}
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return self.sessions[session_id]
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def _get_session_info(self, session_id: str) -> dict:
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"""
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Gets a session given a session ID.
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The session can be used to track data across multiple requests, e.g. for
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interactive authentication.
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"""
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if session_id not in self.sessions:
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session_id = None
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if not session_id:
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# create a new session
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while session_id is None or session_id in self.sessions:
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session_id = stringutils.random_string(24)
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self.sessions[session_id] = {"id": session_id}
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return self.sessions[session_id]
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try:
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return self.sessions[session_id]
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except KeyError:
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raise SynapseError(400, "Unknown session ID: %s" % (session_id,))
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async def get_access_token_for_user_id(
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self, user_id: str, device_id: Optional[str], valid_until_ms: Optional[int]
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@ -1030,11 +1064,8 @@ class AuthHandler(BaseHandler):
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The HTML to render.
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"""
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session = self._get_session_info(session_id)
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# Get the human readable operation of what is occurring, falling back to
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# a generic message if it isn't available for some reason.
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description = session.get("description", "modify your account")
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return self._sso_auth_confirm_template.render(
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description=description, redirect_url=redirect_url,
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description=session["description"], redirect_url=redirect_url,
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)
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def complete_sso_ui_auth(
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@ -1050,8 +1081,6 @@ class AuthHandler(BaseHandler):
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"""
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# Mark the stage of the authentication as successful.
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sess = self._get_session_info(session_id)
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if "creds" not in sess:
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sess["creds"] = {}
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creds = sess["creds"]
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# Save the user who authenticated with SSO, this will be used to ensure
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