azure app proxy to access the on-premise API question

Question

Hi,
I have a Web API hosting in on-premise. now we have a native app needs to call this API from internet, here is what I did

create a app proxy for this on-premise API, follow the article: https://learn.microsoft.com/en-us/azure/active-directory/manage-apps/application-proxy-secure-api-access

using the MSAL library to call this API, the main code fregment is:

-----------------------

IPublicClientApplication clientApp = PublicClientApplicationBuilder
.Create("application id")
.WithDefaultRedirectUri() // will automatically use the default Uri for native app
.WithAuthority("https://login.microsoftonline.com/mytenantid")
.Build();
authResult = await clientApp.AcquireTokenInteractive(scopes).ExecuteAsync();
HttpClient httpClient = new HttpClient();
httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", authResult.AccessToken);
HttpResponseMessage response = await httpClient.GetAsync("https://my-azure-app-proxy-url/api");

-----------------------------------

when call the method await httpClient.GetAsync("https://my-azure-app-proxy-url/api"); it will throw 3 inner exceptions, first exception message is "WebException: The underlying connection was closed: An unexpected error occurred on a send.", second msg is:"IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.", thrid msg is : "SocketException: An existing connection was forcibly closed by the remote host" . i think the resason of these exceptions is the Azure AD can't recognize who am I and redirect me into the sign in page .

and I tried to use the postman to sent the request with the right bearer token, it give the "sign in to your account .." response.

my purpose is very simple, only the authenticated user can access this on-premise API in the internet network. and the on-premise API no need to know who is accessing.

can someone help me on this issue?

Thanks

Answer 1

@admin , Thank you for reaching out. Troubleshooting this issue with being a little difficult over the forum as there might be few nitty-gritty that might get missed while trying to troubleshoot it over the forum posts. Also, the error shared is pretty generic. I would like to check if you have an Azure Support plan to help you create a case with our Technical Support to get you moving ahead and help you in fixing this issue.

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