How to Enable Cross-Origin Resource Sharing (CORS) on IIS7: A Step-by-Step Guide

Enabling Cross-Origin Resource Sharing on IIS7: A Comprehensive Guide

Introduction

Cross-Origin Resource Sharing (CORS) allows resources from one domain to be fetched and utilized by applications from a different origin. To enable CORS on IIS7, follow these steps:

Configuration

1. Add Custom Headers:

   • Navigate to the web.config file for the hosting domain.
   • Add the following custom headers within the <httpProtocol> section:

   <customHeaders>
     <add name="Access-Control-Allow-Origin" value="*" />
     <add name="Access-Control-Allow-Methods" value="GET,PUT,POST,DELETE,OPTIONS" />
     <add name="Access-Control-Allow-Headers" value="Content-Type" />
   </customHeaders>

Troubleshooting

Despite the configuration, if you still receive a 405 response, it may be due to IIS7's handling of HTTP OPTIONS.

Option 1: Modify IIS7 Handler Mappings

1. Open IIS Manager.
2. Navigate to Handler Mappings.
3. Locate "OPTIONSVerbHandler."
4. Change "ProtocolSupportModule" to "IsapiHandler."

5. Set the executable to:

   %windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll

Option 2: Handle OPTIONS Verb in Code

1. Override the BeginRequest method in your application code:

   protected void Application_BeginRequest(object sender,EventArgs e)
   {
       HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*");
   
       if(HttpContext.Current.Request.HttpMethod == "OPTIONS")
       {
           // Handle pre-flight OPTIONS call from browser
           HttpContext.Current.Response.AddHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE");
           HttpContext.Current.Response.AddHeader("Access-Control-Allow-Headers", "Content-Type, Accept");
           HttpContext.Current.Response.AddHeader("Access-Control-Max-Age", "1728000" );
           HttpContext.Current.Response.End();
       }
   }

Conclusion

Enabling CORS on IIS7 requires both configuration updates and potential troubleshooting. By following the steps outlined above, you can empower cross-origin interactions with confidence.

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