Allow a default ITokenRequestCustomizer to be registered

[pgermishuys]

This is useful to ensure that a single TokenRequestCustomizer can be used for various paths such as ITokenRetrievers as well as the HttpContextExtensions.

This introduces a breaking change in Access Token Management's ITokenRequestCustomizer interface, which changed one if it's parameters from HttpRequestMessage to HttpRequestContext. The change was necessary as we want to allow the customizer to be used in the HttpRequestMessageExtensions from which we only get access to the HttpRequest and not the HttpRequestMessage.

The breaking change could be considered ok as the ITokenRequestCustomizer was introduced in Access Token Management 4.1.0 which does not have a non-preview/RC release.

[Copilot]

Pull Request Overview

This PR enables a default ITokenRequestCustomizer to be registered globally and used across multiple token retrieval paths. The primary change is a breaking modification to the ITokenRequestCustomizer interface, which now accepts HttpRequestContext instead of HttpRequestMessage to support customization in contexts where only HttpRequest is available (e.g., HttpContextExtensions).

• Introduced a new HttpRequestContext struct to abstract HTTP request details
• Updated the ITokenRequestCustomizer interface signature to use HttpRequestContext
• Enabled customizer usage in HttpContextExtensions methods (GetUserAccessTokenAsync, GetClientAccessTokenAsync, RevokeRefreshTokenAsync)

Reviewed Changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
HttpRequestContext.cs	New struct to represent HTTP request context with method, URI, and headers
ITokenRequestCustomizer.cs	Changed interface parameter from HttpRequestMessage to HttpRequestContext
HttpRequestContextExtensions.cs (AccessTokenManagement)	Extension method to convert HttpRequestMessage to HttpRequestContext
HttpRequestContextExtensions.cs (OpenIdConnect)	Extension method to convert HttpRequest to HttpRequestContext
HttpContextExtensions.cs	Added logic to apply token request customization in extension methods
ClientCredentialsTokenRetriever.cs	Updated to use new HttpRequestContext when calling customizer
OpenIdConnectUserAccessTokenRetriever.cs	Updated to use new HttpRequestContext when calling customizer
OpenIdConnectClientAccessTokenRetriever.cs	Updated to use new HttpRequestContext and fixed parameter merging logic
Test files	Updated tests to reflect new interface signature and added comprehensive test coverage for the new functionality
Public API verification files	Updated to reflect new public HttpRequestContext type and interface changes

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