How to create a sample self-signed certificate with SAN using OpenSSL

Issue:

Modern web browsers require a Subject Alternative Name (SAN) in SSL/TLS certificates. The Common Name (CN) field, historically used for hostname verification, is deprecated due to compatibility and security concerns. Browsers reject certificates lacking SAN with errors like: “Certificate is not valid for the name.”

Affected Version/Platforms: Chrome 58 and later, Firefox, and other modern web browsers.

Resolution: To create an sample SSL/TLS certificate for testing purposes with a Subject Alternative Name (SAN), follow these steps:

1. Create the san.cnf Configuration File:

2. Generate the CSR and Private Key:

3. (Optional) Verify SAN Entries:

4. Create the Self-Signed Certificate:

Prevention: In case there are issues with a certificate provided from a CA, testing with a self signed certificate can help with the troubleshooting process.