AzureIdentityAuthenticationHandler.cs

using Azure.Core;

namespace Sandbox;

public sealed class AzureIdentityAuthenticationHandler(TokenCredential tokenCredential) : DelegatingHandler
{
    public static HttpRequestOptionsKey<TokenRequestContext> TokenRequestContextKey => new(key: nameof(TokenRequestContext));

    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage httpRequestMessage,
        CancellationToken cancellationToken
    ) {
        if (httpRequestMessage.Options.TryGetValue(
            key: TokenRequestContextKey,
            value: out var tokenRequestContext
        )) {
            var accessToken = await tokenCredential
                .GetTokenAsync(
                    cancellationToken: cancellationToken,
                    requestContext: tokenRequestContext
                )
                .ConfigureAwait(continueOnCapturedContext: false);

            httpRequestMessage.Headers.Authorization = new(
                parameter: accessToken.Token,
                scheme: "Bearer"
            );
        }

        return await base
            .SendAsync(
                cancellationToken: cancellationToken,
                request: httpRequestMessage
            )
            .ConfigureAwait(continueOnCapturedContext: false);
    }
}