How to generate SSL Certificates for testing a Sample Application?

Your Application Server must run on a secured Web Server; hence, use a valid SSL certificate for your domain and use it to configure your Web Service to make your domain accessible on HTTPS. 

Alternatively, you may also use a self-signed certificate to run the Application Server. Some of the websites that generate self-signed certificates are: 

• https://letsencrypt.org/ 
• https://www.sslchecker.com/csr/self_signed 
• https://www.akadia.com/services/ssh_test_certificate.html