testssl generate self signed certificates for local development purposes.

• generates wildcard x509 certificates which covers *.domain.tld and domain.tld.
• outputs root authority and domain/server CA
• 10 years validity
• fallback to use .test as TLD if you don't input any specific TLD (https://tools.ietf.org/html/rfc6761)

• testssl --domain=example - generates CA for example.test in ssl subfolder
• testssl --domain=mylocal.loc --dir=site - generates CA for mylocal.loc in folder site
• testssl --domain=mydoman.test --dir= - does not output any files
• ssl.GenerateCert("mydomain_name", "") - if you use from other package but don't want to generate files

• import root CA in your browser
• Firefox -> open in browser tab about:preferences#privacy, click View Certificates and click Import -> select rootCA.pem
• Chrome -> open in browser tab chrome://settings/certificates?search=authorities and click Import -> select rootCA.pem

or

• MacOS - import PEM trough keychain on MacOS and mark as trusted
• Ubuntu - as root CA on Ubuntu (you need to convert PEM to CRT). openssl x509 -in rootCA.pem -inform PEM -out rootCA.crt