.Net core Web API who calls other external APIs

Question

I'm creating a .Net Core web API which will further call an external API.

Scenario:

In .Net Core web API, I want to make a Post request to UiPath Orchestrator API to get authentication token. Following is the link for the Request that I want to make https://postman.uipath.rocks/#8f3b38d8-57dc-4d79-876d-0d2ff897f61a

[HttpPost]
public Task<IActionResult> GetAccessToken()
{
  //Here I want to make a Post request to the API to Authenticate
}

And response (Auth token) of this will be sent to another post request to start a process https://postman.uipath.rocks/#738c3beb-1c19-4257-8474-841a054c4220

[HttpPost]
 public Task<IActionResult> StartProcess(string token)
 {
   //Here I want to make a Post request to the other API in which token from the previous call will be 
    sent in header
 }

I have to complete it in a day or two and I can't figure out how can I achieve this.

Any help will be much appreciated.

https://learn.microsoft.com/en-us/dotnet/api/system.net.http.httpclient?view=net-5.0# — Artur, Mar 28 '21 at 20:35

score 4 · Answer 1 · answered Mar 28 '21 at 21:50

If I correctly understand you want to have an endpoint, which will make two POST requests to third-party API. The first request will retrieve an Authorization Token. The second request will use the Token in its Headers to pass an authorization.

To achive this behavior, you should to have a single endpoint in your API, instead of two endpoints (as in your example above).

Also, I recommend you to have a separate class, which will responsible for communicating with your third-party API (with the postman.uipath.rocks).

So, your single endpoint to call a third-party API may looks like this:

public class Controller
{
    // another Controller's code...
    private readonly IPostmanApi postmanApi;

    public Controller(IPostmanApi postmanApi)
    {
        this.postmanApi = postmanApi;
    }

    [HttpPost]
    public async Task<IActionResult> StartPostmanProcess()
    {
        string token = await postmanApi.GetToken();
        await postmanApi.StartProcess(token);

        return Accepted();
    }

    // another Controller's code...
}

Your IPostmanApi.cs file may looks like this:

public interface IPostmanApi
{
    ///<summary>
    /// A method to get Authorization Token from Postman
    ///</summary>
    Task<string> GetToken();

    ///<summary>
    /// A method to get start a process in Postman
    ///</summary>
    ///<param name="token">Postman's authorization token</param>
    Task StartProcess(string token);
}

Your PostmanApi.cs file may looks like this:

public class PostmanApi
{
    Task<string> GetToken()
    {
        using (HttpClient client = new HttpClient())
        {
            var response = await client.PostAsync("https://postman.uipath.rocks/#8f3b38d8-57dc-4d79-876d-0d2ff897f61a");

            // Note: this code assumes that the whole response body is a string Token.
            // If the `postman.uipath.rocks` returns an JSON object, which contains a
            // Token inside some field, you may use Newtonsoft.Json library to deserialize
            // it, and then retrieve your Token from corresponding field.
            // See example here: https://stackoverflow.com/questions/24131067/deserialize-json-to-array-or-list-with-httpclient-readasasync-using-net-4-0-ta
            return await response.Content.ReadAsStringAsync();
        }
    }

    Task StartProcess(string token)
    {
        using (HttpClient client = new HttpClient())
        {
            // Note: this code assumes that the `postman.uipath.rocks` receives
            // a **Bearer** token. If it receives another kind of authentication
            // scheme, you should use it instead of "Bearer".
            client.DefaultRequestHeaders.Authorization 
                         = new AuthenticationHeaderValue("Bearer", token);
            await client.PostAsync("https://postman.uipath.rocks/#738c3beb-1c19-4257-8474-841a054c4220");
    }
}

Also don't forget to register your IPostmanApi service within Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    // another code...

    services.AddScoped<IPostmanApi, PostmanApi>();
    // another code...
}

Notice:

This code is not thread-safe (because an HttpClient is not thread safe). If you want it to be thread-safe, consider to use IHttpClientFactory.

Useful links:

.Net core Web API who calls other external APIs

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