fix: allow parsing of certificate chains and password-less certificates

[handsomejack-42]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Certificate parsing function isn't capable of parsing certificate chains

The decodePksc12 function fails to parse my PKCS12 certificate chain with the message

decoding the client certificate: decoding the PKCS#12 client certificate: pkcs12: expected exactly two safe bags in the PFX PDU

because, internally, it uses the pkcs12.Decode function, which expects only the key and a main cert, not a whole chain of certs. It is mentioned in the comment that

Since PKCS#12 files often contain more than one certificate, you probably want to use [DecodeChain] instead.

The option is either switching to that .DecodeChain function, or, there is a cert parser implemented in azidentity, that provides even more (PEM) parsing capabilities.

I propose using the parsing function from azidentity instead, as that is the 'native' identity provider for azure anyway.

Password-less certificates

When parsing the config into credential providers in NewAuthProvider, the only way to trigger the certificate credential path is to have password protected certificate. Certificates can exist without password protection.

Remove this condition to allow even password-less certificates.

Which issue(s) this PR fixes:

x

Special notes for your reviewer:

x

Does this PR introduce a user-facing change?

Added certificate parsing capability for password-less certificates and certificate chains

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[k8s-ci-robot]

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[MartinForReal]

Thanks for the fix!
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: handsomejack-42, MartinForReal

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[MartinForReal]

/ok-to-test

[handsomejack-42]

sub 50m approve and merge, wow!

kudos @MartinForReal