docs: def HA1(realm, username, password, algorithm):
      """Create HA1 hash by realm, username, password
  
      HA1 = md5(A1) = MD5(username:realm:password)
      """
      if not realm:
          realm = u''
      return H(b":".join([username.encode('utf-8'),
                             realm.encode('utf-8'),
                             password.encode('utf-8')]), algorithm)