Create a custom proxy endpoint action with ASP.NET Core MVC

 1// Controller to handle proxy requests
 2public class SampleProxyController : Controller
 3{
 4    // Dependency injection for IHttpClientFactory to create HttpClient instances
 5    private readonly IHttpClientFactory _httpClientFactory;
 6
 7    // Constructor to initialize the IHttpClientFactory instance
 8    public SampleProxyController(IHttpClientFactory httpClientFactory)
 9    {
10        _httpClientFactory = httpClientFactory;
11    }
12
13    // Action method that proxies the request
14    public async Task<IActionResult> Proxy()
15    {
16        // The target proxy URI. This can be dynamically set or statically defined.
17        Uri proxyUri = new("https://myproxyurl/endpoint"); // your config
18
19        // Enforce the HTTP version for the request to HTTP/2
20        Version proxyHttpVersion = new("2.0"); // your config
21
22        // Get the incoming request from the client
23        HttpRequest sourceRequest = this.Request;
24
25        // Extract the query string from the source request, if any
26        string? queryString = sourceRequest.QueryString.Value ?? null;
27
28        // Build the target URI, appending the query string if it exists
29        UriBuilder uriBuilder = new(proxyUri);
30        if (queryString is not null)
31        {
32            uriBuilder.Query = queryString;
33        }
34        Uri targetUri = uriBuilder.Uri;
35
36        // Create a new HTTP request message for the proxy target
37        HttpRequestMessage proxyRequestMessage = new()
38        {
39            RequestUri = targetUri,
40            Method = new HttpMethod(sourceRequest.Method), // Use the HTTP method from the source request
41            Version = proxyHttpVersion
42        };
43
44        // Forward headers from the source request, except the "Cookie" header
45        foreach (KeyValuePair<string, StringValues> header in sourceRequest.Headers)
46        {
47            if (!string.Equals(header.Key, "Cookie", StringComparison.OrdinalIgnoreCase))
48            {
49                proxyRequestMessage.Headers.TryAddWithoutValidation(header.Key, header.Value.ToList());
50            }
51        }
52
53        // Set the Host header to match the target URI's authority
54        proxyRequestMessage.Headers.Host = targetUri.Authority;
55
56        // Add the X-Forwarded-For header to indicate the client's IP address
57        IPAddress? requestIPAddress = sourceRequest.HttpContext.Connection.RemoteIpAddress;
58        proxyRequestMessage.Headers.TryAddWithoutValidation("X-Forwarded-For", requestIPAddress?.ToString());
59
60        // Forward the body of the source request to the proxy target
61        proxyRequestMessage.Content = new StreamContent(sourceRequest.Body);
62        if (sourceRequest.Headers.TryGetValue("Content-Type", out StringValues value))
63        {
64            string? contentType = value;
65            if (contentType is not null)
66            {
67                proxyRequestMessage.Content.Headers.ContentType = new MediaTypeHeaderValue(contentType);
68            }
69        }
70
71        // Create an HttpClient instance using the factory and send the proxy request
72        HttpClient httpClient = _httpClientFactory.CreateClient("YourClientProxyNameHere"); // replace this with your config
73        HttpResponseMessage proxyResponse = await httpClient.SendAsync(proxyRequestMessage).ConfigureAwait(false);
74
75        // Add CORS headers to allow cross-origin requests if required
76        sourceRequest.HttpContext.Response.Headers.AddIfNotExists("Access-Control-Allow-Origin", sourceRequest.Headers.Origin.FirstOrDefault() ?? "*");
77        sourceRequest.HttpContext.Response.Headers.AddIfNotExists("Access-Control-Allow-Headers", "content-type");
78        sourceRequest.HttpContext.Response.Headers.AddIfNotExists("Access-Control-Allow-Credentials", "true");
79
80        // Read the response content and its type from the proxy response
81        string proxyResponseContent = await proxyResponse.Content.ReadAsStringAsync();
82        string? proxyResponseContentType = proxyResponse.Content.Headers.ContentType?.ToString();
83
84        // Return the response from the proxy target as the result of this action
85        return new ContentResult
86        {
87            StatusCode = (int)proxyResponse.StatusCode, // Use the same status code as the proxy response
88            Content = proxyResponseContent, // Forward the response content
89            ContentType = proxyResponseContentType // Set the content type
90        };
91    }
92}