Microsoft Graph SDK should make the content of the WWW-Authenticate header available in the request context to support Pop with server nonce.

Please provide the following (and please check them off the list with [x]) before submitting this issue:

• [ x ] Expected behavior. Please provide links to the specific Microsoft Graph documentation you used to determine the expected behavior.
• [ x ] Actual behavior. Provide error codes, stack information, and a Fiddler capture of the request and response (please remove personally identifiable information before posting).
• Steps to reproduce the behavior. Include your code, IDE versions, client library versions, and any other information that might be helpful to understand your scenario.

As tenant admins will enable Pop with server nonce for Microsoft Graph, the Clients will need to parse the WWW-Authenticate header to retrieve the Nonce and other parameters.

Actual behavior

Today, the WWW-Authenticate header is parsed by the AuthenticationHandler to provide the claims in the CaeAuthenticationProviderOption for the implementations of IAuthenticationProvider to support CAE.

Expected behavior

For Pop, the claims won't be enough. We need to provide the whole content of the WWW-Authenticate header (assuming Microsoft graph retuns only one WWW-Authenticate header), so that MSAL, or the classes that will provide the authentication can parse it and provide the authorization header (for instance Pop)

Steps to reproduce the behavior

Start with src/Microsoft.Graph.Core/Requests/Middleware/AuthenticationHandler.cs, especially the linked section that parses WWW-Authenticate for CaeAuthenticationProviderOption. Trace how that information reaches IAuthenticationProvider implementations and determine where the full header content should be exposed in the request context. Done means authentication implementations can retrieve the header's Nonce and other parameters for Microsoft Graph POP support.