Fixes: #8088
Previously we would perform OIDC discovery on startup,
which involves making HTTP requests to the identity provider(s).
If that took a long time, we would block startup.
If that failed, we would crash startup.
This commit:
- makes the loading happen in the background on startup
- makes an error in the 'preload' non-fatal (though it logs at CRITICAL
for visibility)
- adds a templated error page to show on failed redirects (for
unavailable providers), as otherwise you get a JSON response in your
navigator.
- This involves introducing 2 new exception types to mark other
exceptions and keep the error handling fine-grained.
The machinery was already there to load-on-demand the discovery config,
so when the identity provider
comes back up, the discovery is reattempted and login can succeed.
Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>
This way we actually detect problems like
https://github.com/element-hq/synapse/pull/19475 as they happen instead
of being invisible until something breaks.
Sanity check that Complement is testing against your code changes
(whether it be local or from the PR in CI).
```
COMPLEMENT_DIR=../complement ./scripts-dev/complement.sh --in-repo -run TestSynapseVersion
```
