Enabling session_lifetime in the configuration prevents registration of guest users

[matrixbot]

This issue has been migrated from #12440.

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Description

When the configuration option session_lifetime (used to log out users after sign in after a certain amount of time) is used, attempts to register as a guest user will fail due to a 500 Internal Server Error because of a python exception.

Steps to reproduce

• Enable configuration option session_lifetime to something like 30d
• Host the Element client which points to the homeserver by default (set within config.json for Element)
• Observe the 'Explore Rooms' button not showing under the Sign In and Create Account button, and the POST request Element makes to register a Guest account fail with a response code of 500 Internal Server Error

I was trying to get the Explore Room button to work in Element.
After lots of digging around to, well, not much useful. I then found that the POST request to /_matrix/client/r0/register?kind=guest responds with a 500 Internal Server Error status code, shows an exception in homeserver.log, and which prevented the button from showing up.

Expectation: Even with the session_lifetime option, guest users can be registered (what happens with session_lifetime really depends)

homeserver.log:

2022-04-11 20:57:46,503 - synapse.access.http.8008 - 427 - INFO - GET-71697 - ***.***.***.*** - 8008 - {None} Processed request: 0.001sec/0.001sec (0.001sec, 0.000sec) (0.000sec/0.000sec/0) 558B 200 "GET /_matrix/client/versions HTTP/1.0" "***********************************************************************************************************" [0 dbevts]
2022-04-11 20:57:46,786 - synapse.handlers.register - 358 - INFO - POST-71699 - Skipping auto-join for @113:jacksonchen666.com because auto-join for guests is disabled
2022-04-11 20:57:46,787 - synapse.http.server - 100 - ERROR - POST-71699 - Failed handle request via 'RegisterRestServlet': <XForwardedForRequest at 0x7f81c6432350 method='POST' uri='/_matrix/client/r0/register?kind=guest' clientproto='HTTP/1.0' site='8008'>
Traceback (most recent call last):
  File "/home/matrix-synapse/synapse/env/lib/python3.10/site-packages/synapse/http/server.py", line 268, in _async_render_wrapper
    callback_return = await self._async_render(request)
  File "/home/matrix-synapse/synapse/env/lib/python3.10/site-packages/synapse/http/server.py", line 470, in _async_render
    callback_return = await raw_callback_return
  File "/home/matrix-synapse/synapse/env/lib/python3.10/site-packages/synapse/rest/client/_base.py", line 99, in wrapped
    return await orig(*args, **kwargs)
  File "/home/matrix-synapse/synapse/env/lib/python3.10/site-packages/synapse/rest/client/register.py", line 451, in on_POST
    ret = await self._do_guest_registration(body, address=client_addr)
  File "/home/matrix-synapse/synapse/env/lib/python3.10/site-packages/synapse/rest/client/register.py", line 849, in _do_guest_registration
    ) = await self.registration_handler.register_device(
  File "/home/matrix-synapse/synapse/env/lib/python3.10/site-packages/synapse/handlers/register.py", line 768, in register_device
    res = await self._register_device_client(
  File "/home/matrix-synapse/synapse/env/lib/python3.10/site-packages/synapse/handlers/register.py", line 812, in register_device_inner
    raise Exception(
Exception: session_lifetime is not currently implemented for guest access
2022-04-11 20:57:46,790 - synapse.access.http.8008 - 427 - INFO - POST-71699 - ***.***.***.*** - 8008 - {None} Processed request: 0.023sec/0.001sec (0.007sec, 0.000sec) (0.001sec/0.016sec/2) 55B 500 "POST /_matrix/client/r0/register?kind=guest HTTP/1.0" "*************************************************************************************************" [0 dbevts]

Version information

• Homeserver: https://matrix.jacksonchen666.com

If not matrix.org:

• Version: 1.55.2 updated to 1.56.0 since then (tested, issue persists)

• Install method: pip install matrix-synapse[postgres] (with the python virtual environment located at /home/matrix-synapse/synapse/env/, with a nginx reverse proxy & delegation)

• Platform: Linux, Fedora 35, Not within a container or VM