发送Ajax POST请求时遭遇401 Unauthorized错误求助

Hey Willie, sorry to hear you're hitting that frustrating 401 Unauthorized error when testing your POST Ajax call in Visual Studio 2015-2017. Let's walk through targeted checks to get to the bottom of this—since you've already tried existing Stack Overflow solutions, we'll dig into less obvious angles too.

You're working on a simple POST Ajax implementation in VS 2015-2017, but every request returns a 401 Unauthorized error (see attached screenshot: [401 Error Screenshot]). You've shared your client-side code, server-side code, and web.config settings, and tried standard Stack Overflow fixes without luck. You've also provided full step-by-step operation screenshots to help diagnose the issue.

Let's break down potential issues by component:

1. web.config Authentication & Authorization Settings #

First, verify your config isn't blocking anonymous or authenticated POST requests:

• Check your authentication mode:

  <!-- Example Windows Auth -->
  <authentication mode="Windows" />
  <!-- OR Forms Auth -->
  <authentication mode="Forms">
    <forms loginUrl="~/Account/Login" timeout="2880" />
  </authentication>
  

  If using Windows Auth, your Ajax request needs to pass credentials. If using Forms, ensure the auth cookie is being sent.
• Inspect the <authorization> node—if you have <deny users="?" />, your server method must allow anonymous access (via [AllowAnonymous]) or the request must include valid auth tokens.
• For Web API, confirm you haven't enabled global authorization filters that block unauthenticated requests.

2. Client-Side Ajax Request Configuration #

Double-check your Ajax call for common credential or formatting issues:

$.ajax({
  url: '/api/YourController/YourAction',
  type: 'POST',
  data: JSON.stringify(yourPayload),
  contentType: 'application/json',
  // Critical for passing auth credentials (Windows/Forms)
  withCredentials: true,
  success: function(response) { /* ... */ },
  error: function(xhr) { console.log(xhr.statusText); }
});

• Ensure withCredentials: true is set if your server expects auth cookies/tokens (especially for Windows Auth in intranet scenarios).
• Verify the request URL matches your server's routing (e.g., Web API uses api/Controller/Action by default, MVC uses Controller/Action).
• Confirm contentType: 'application/json' is present if your server uses [FromBody] to bind the payload—missing this can trigger unexpected auth checks.

3. Server-Side Code Validation #

Check your controller/method for auth-related restrictions:

// Web API Controller Example
public class YourApiController : ApiController
{
  // Add [AllowAnonymous] if this method should accept unauthenticated requests
  [HttpPost]
  [AllowAnonymous]
  public IHttpActionResult YourPostAction([FromBody] YourModel model)
  {
    // ... your logic
    return Ok(result);
  }
}

// MVC Controller Example
public class YourMvcController : Controller
{
  [HttpPost]
  [AllowAnonymous] // Required if authorization denies anonymous users
  public ActionResult YourPostAction(YourModel model)
  {
    // ... your logic
    return Json(result);
  }
}

• If you haven't added [AllowAnonymous], anonymous requests will be blocked with 401—even if you thought the method was open.
• Ensure the [HttpPost] attribute is present—missing it can lead to routing mismatches that might be interpreted as unauthorized access.
• Check for custom action filters or global auth filters that might be overriding your method-level settings.

4. Visual Studio Debug Environment Quirks #

VS's local debug setup (IIS Express) sometimes has hidden auth settings:

• Right-click your project → Properties → Web → Authentication: Confirm the selected auth mode matches your web.config (e.g., Windows Auth enabled if that's what you're using).
• Open IIS Express's config file (%USERPROFILE%\Documents\IISExpress\config\applicationhost.config) and verify the <authentication> settings for your site match your project's config—sometimes IIS Express overrides project settings.
• Clean your solution, rebuild, and clear your browser's cache/cookies (old auth cookies can cause unexpected 401s).

5. Deep Dive with Server Logs #

If all else fails, check IIS logs (for IIS Express, logs are in %USERPROFILE%\Documents\IISExpress\Logs)—look for entries with 401 status codes. The substatus code will tell you exactly why the auth failed:

• 401.1: Login failed
• 401.2: Server config issue
• 401.3: ACL denied access
• 401.4: Filter denied access

This will give you a precise clue about whether the issue is credential-related, config-related, or permission-related.

内容的提问来源于stack exchange，提问作者Willie Cheng