code: func (dk *BasicDockerKeyring) Lookup(image string) ([]docker.AuthConfiguration, bool) {
  	// range over the index as iterating over a map does not provide a predictable ordering
  	ret := []docker.AuthConfiguration{}
  	for _, k := range dk.index {
  		// both k and image are schemeless URLs because even though schemes are allowed
  		// in the credential configurations, we remove them in Add.
  		if matched, _ := urlsMatchStr(k, image); !matched {
  			continue
  		}
  
  		ret = append(ret, dk.creds[k]...)
  	}
  
  	if len(ret) > 0 {
  		return ret, true
  	}
  
  	// Use credentials for the default registry if provided, and appropriate
  	if isDefaultRegistryMatch(image) {
  		if auth, ok := dk.creds[defaultRegistryHost]; ok {
  			return auth, true
  		}
  	}
  
  	return []docker.AuthConfiguration{}, false
  }
docs: // Lookup implements the DockerKeyring method for fetching credentials based on image name.
  // Multiple credentials may be returned if there are multiple potentially valid credentials
  // available.  This allows for rotation.