code: def _process_cross_domain_request(cls, request, response):
          
  
          # Step 1
          # Check for Origin header.
          origin = request.get('Origin')
          if not origin:
              return
  
          # Step 2
          # Check if the origin is in the list of allowed origins.
          if not (origin in cls.meta.http_allowed_origins or
                  '*' == cls.meta.http_allowed_origins):
              return
  
          # Step 3
          # Try to parse the Request-Method header if it exists.
          method = request.get('Access-Control-Request-Method')
          if method and method not in cls.meta.http_allowed_methods:
              return
  
          # Step 4
          # Try to parse the Request-Header header if it exists.
          headers = request.get('Access-Control-Request-Headers', ())
          if headers:
              headers = [h.strip() for h in headers.split(',')]
  
          # Step 5
          # Check if the headers are allowed on this resource.
          allowed_headers = [h.lower() for h in cls.meta.http_allowed_headers]
          if any(h.lower() not in allowed_headers for h in headers):
              return
  
          # Step 6
          # Always add the origin.
          response['Access-Control-Allow-Origin'] = origin
  
          # TODO: Check if we can provide credentials.
          response['Access-Control-Allow-Credentials'] = 'true'
  
          # Step 7
          # TODO: Optionally add Max-Age header.
  
          # Step 8
          # Add the allowed methods.
          allowed_methods = ', '.join(cls.meta.http_allowed_methods)
          response['Access-Control-Allow-Methods'] = allowed_methods
  
          # Step 9
          # Add any allowed headers.
          allowed_headers = ', '.join(cls.meta.http_allowed_headers)
          if allowed_headers:
              response['Access-Control-Allow-Headers'] = allowed_headers
  
          # Step 10
          # Add any exposed headers.
          exposed_headers = ', '.join(cls.meta.http_exposed_headers)
          if exposed_headers:
              response['Access-Control-Expose-Headers'] = exposed_headers
docs: Facilitate Cross-Origin Requests (CORs).