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>
