Use Saml2Aws CLI as an alternative to SAML to AWS STS Key Conversion.

Install on Mac.

brew install saml2aws
saml2aws --version

Configure. Provide information.

saml2aws configure

It will create a ~/.saml2aws config file. Set session to 8 hours.

aws_session_duration    = 28800

Login.

saml2aws login

After authentication and/or MFA, your ~/.aws/credentials will be updated.