Adding support for az login --identity

Program.cs

@@ -22,4 +22,23 @@
     };
 });
 
+// Can be consumed by "az login --identity" by specifying MSI_ENDPOINT environment variable to this action URL
+// https://github.com/Azure/msrestazure-for-python/blob/master/msrestazure/azure_active_directory.py#L474
+
+app.MapPost("/token", async (HttpContext context, HttpRequest request) =>
+{
+    var form = await request.ReadFormAsync();
+    var resource = form["resource"].ToString();
+    var token = await tokenCredential.GetTokenAsync(new TokenRequestContext(new[] { resource }));
+    context.Response.Headers.Add("Content-Type", "application/json"); // Set the Content-Type header to JSON
+    return new Dictionary<string, string>
+    {
+        ["access_token"] = token.Token,
+        ["expiresOn"] = token.ExpiresOn.ToString("O", CultureInfo.InvariantCulture),
+        ["expires_on"] = token.ExpiresOn.ToUnixTimeSeconds().ToString(),
+        ["token_type"] = "Bearer",
+        ["resource"] = resource
+    };
+});
+
 app.Run();

README.md

@@ -35,6 +35,8 @@ services:
     environment:
       - "IDENTITY_ENDPOINT=http://azclicredsproxy:8080/token"
       - "IMDS_ENDPOINT=dummy_required_value"
+      # Specify MSI_ENDPOINT below if using "az login --identity" in your service.
+      - "MSI_ENDPOINT=http://azclicredsproxy:8080/token"
 ```
 
 
@@ -65,6 +67,9 @@ Then, we must add two environment variables to each service:
 
 With these two environment variables, any service that uses `DefaultAzureCredential` or `ManagedIdentityCredential` will now call the proxy when Azure credentials are needed. This is because one of `ManagedIdentityCredential`'s [source implementations](https://github.com/Azure/azure-sdk-for-net/blob/Azure.Identity_1.6.0/sdk/identity/Azure.Identity/src/AzureArcManagedIdentitySource.cs) explicitly looks for both of these environment variables if they are specified.
 
+> [!NOTE]
+> If you are using using `az cli` in your service and your service wants to do `az login --identity` then specify `MSI_ENDPOINT`: the URL of the proxy endpoint (e.g., `http://azclicredsproxy:8080/token`) environment variable instead. `IDENTITY_ENDPOINT` and `IMDS_ENDPOINT` are not required for `az login --identity`.
+
 With this proxy, Dockerfiles can remain untouched and production-ready. The proxy can easily be added to an existing `docker-compose.yml`, and the environment variables are also easy to add. Now, the containerized environment looks like this:
 
 <img src="https://user-images.githubusercontent.com/14242083/224446855-35880df8-1ccd-42df-b226-5afa7b93caa6.png" width="800" />