Support of AuthFlow without client secret

[ganapathysuresh]

Is your feature request related to a problem? Please describe. Azure Identity support ClientSecretCredential which is used to get token by supplying client secret. This is good for a confidential client. But for public client, we need to support the method of getting token without supplying the client secret

Describe the solution you'd like A new class derived from TokenCredential should be implemented which needs only Tenant id, client id and redirection url and the public client flow will be implemented in this new class , say PublicClientCredential

Describe alternatives you've considered This is only method inline with other TokenCredentials. So alternative considered as that will violate existing TokenCredentails

Additional context We need to attempt C# equivalent of PublicClientConfigurationBuilder. Also we may attempt to optionally support .NET feature of "withBroker" feature to support SSO

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