Implementing Mutual TLS (mTLS) Authentication with OpenSSL: A Step-by-Step Guide
This article explores mutual Transport Layer Security (mTLS) authentication and how OpenSSL can facilitate its implementation. Also known as client-server authentication, mTLS is a robust security mechanism that requires both the client and server to present valid digital certificates before establishing a secure connection. This additional layer of authentication ensures that only trusted entities can access protected resources.
We will set up mutual TLS (mTLS) using two intermediate CAs—one for server certificates and another for client certificates—both signed by the same root CA.
Steps Overview:
- Create Root CA
- Create Two Intermediate CAs (one for server, one for client)
- Generate Server Certificate (signed by Server Intermediate CA)
- Generate Client Certificate (signed by Client Intermediate CA)
- Start OpenSSL Server with mTLS
- Test with curl