MQTTNet — Broker and Client with TLS (OpenSSL) in C#
Steps to create a broker (MQTTNet) with TLS support in C#/.NET that actually works.
Mar 28, 2024 · 1 min read · Som
MQTT is the workhorse protocol for IoT messaging, and MQTTNet is the go-to library on .NET. The tricky part is wiring up TLS correctly so broker and client actually complete the handshake.
The pieces
- Generate certificates with OpenSSL (CA, server, and optionally client).
- Configure the broker to present the server certificate over TLS.
- Configure the client to trust the CA and connect on the secure port.
Certificate essentials
Get the certificate chain and the server's Common Name / SAN right — most "handshake failed" errors trace back to a name mismatch or an untrusted CA, not to the code.
Takeaway
Once certificates are correct, MQTTNet's TLS options are a few lines. Treat the PKI setup as the real task and the C# wiring becomes straightforward.