Adding support for certificate based credentials for app authentication

[msabansal]

The implementation is inspired by the implementation of client_secret_credential.

[heaths]

Great start! Could you also add an example / test for this crate like with other credentials? It would be expected that a customer provide their own certificate so that wouldn't need to be part of the sample, of course. But this also helps make sure it works as expected.

[msabansal]

@heaths Thanks for reviewing the PR and providing feedback. I have added an example and fixed the comments.

[msabansal]

I have added an example. If there is some test infra i am happy to write a test aswell.

[bmc-msft]

Can this be an optional feature? There are occasions where linking against OpenSSL is a significant hurdle.

[msabansal]

@bmc-msft I agree. I realized this yesterday when i was building in a CI/CD pipeline 👍

[heaths]

LGTM, apart from a crate-specific feature name of client_certificate as opposed to an implementation detail like openssl.

[msabansal]

The error i see is in security_keyvault crate which i have not changed (but imported). Do i need to fix it?

[bmc-msft]

@msabansal , pr #719 will address the issues you're experiencing.

[heaths]

Thanks!