I use a simple Flask server for personal use. I use self-signed certificates because for some reason plain HTTP no longer works. I start the server with a command

http_server = WSGIServer(('', 443), app, keyfile='server.key', certfile='server.crt')

Of course, I have to tell my browser to ignore the certificate warning, which is fine. What I do not like is that my server sends me this error message:

ssl.SSLError: [SSL: SSLV3_ALERT_CERTIFICATE_UNKNOWN] sslv3 alert certificate unknown (_ssl.c:992)

Is there a way to suppress this error?

Would you perhaps also suggest creating a suitable CA certificate and is this possible for free for certificates with a longer duration (I do not want to renew the certificate every three months for personal use).