[identity] Use environment variable for password for PEM

[mpodwysocki]

Packages impacted by this PR

• [identity]

Issues associated with this PR

• EnvironmentCredential supports certificate passwords #22053

Describe the problem that is addressed by this PR

Adds support for the AZURE_CLIENT_CERTIFICATE_PASSWORD environment variable to allow a PEM certificate with a password.

What are the possible designs available to address the problem? If there are more than one possible design, why was the one in this PR chosen?

As documented in the MSAL Library for creating certificate credentials, we have to decode the private key with the following code:

const privateKeyObject = crypto.createPrivateKey({
    key: privateKeySource,
    passphrase: "password", // enter your certificate passphrase here
    format: 'pem'
});

const privateKey = privateKeyObject.export({
    format: 'pem',
    type: 'pkcs8'
});

Are there test cases added in this PR? (If not, why?)

• Added a PEM with password and added test for checking for password.

Provide a list of related PRs (if any)

Command used to generate this PR:**(Applicable only to SDK release request PRs)

Checklists

• Added impacted package name to the issue description
• Does this PR needs any fixes in the SDK Generator?** (If so, create an Issue in the Autorest/typescript repository and link it here)
• Added a changelog (if necessary)

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-identity