code: func (c *Cors) areHeadersAllowed(requestedHeaders []string) bool {
  	if c.allowedHeadersAll || len(requestedHeaders) == 0 {
  		return true
  	}
  	for _, header := range requestedHeaders {
  		header = http.CanonicalHeaderKey(header)
  		found := false
  		for _, h := range c.allowedHeaders {
  			if h == header {
  				found = true
  			}
  		}
  		if !found {
  			return false
  		}
  	}
  	return true
  }
docs: // areHeadersAllowed checks if a given list of headers are allowed to used within
  // a cross-domain request.