The Open Source Security Foundation (OpenSSF) has developed free courses for software developers on how to develop secure software.
Free Course via LF Training & Certification
The “Developing Secure Software” (LFD121) course is available on the Linux Foundation Training & Certification platform. It focuses on the fundamentals of developing secure software. Both the course and certificate of completion are free. It is entirely online, takes about 14-18 hours to complete, and you can go at your own pace. Those who complete the course and pass the final exam will earn a certificate of completion valid for two years.