mTLS support for Android

[Darin755]

Pre-submission Checks

• I checked for similar issues, but could not find any. I also checked the closed issues. I could not contribute additional information to any existing issue.
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Feature description

Right now the owncloud mobile app throws an error when attempting to connect to a server using mTLS for authentication.

Proposed solution

Instead of throwing an error, it should use existing Android APIs to use a client cert from the system. This is already supported by many other apps since Android is the one doing the heavy lifting.

Alternative solutions you considered

Using a web browser since web browsers natively support it.

Additional context

No response

[DeepDiver1975]

There is currently very limited request of such a feature.