code: public String generateJwt() throws NexmoUnacceptableAuthException {
          JWTAuthMethod authMethod = this.httpWrapper.getAuthCollection().getAuth(JWTAuthMethod.class);
          return authMethod.constructToken(System.currentTimeMillis() / 1000L, JWTAuthMethod.constructJTI());
      }
docs: Generate a JWT for the application the client has been configured with.
  
  @return A String containing the token data.
  
  @throws NexmoUnacceptableAuthException if no {@link JWTAuthMethod} is available