When running aws-mfa-login without a configuration file this is output:
% aws-mfa-login
2022/07/25 13:30:44 Config File ".aws-mfa" Not Found in "[/Users/asmodai]"
This should be .aws-mfa.yaml. I think it's the viper line at cmd/root.go#L61. Unsure at this point if this is a bug in aws-mfa-login's use of viper or viper itself.
Even adding viper.SetConfigType("yaml") after that line does nothing to change the output. But I am not that familiar with viper and its use, so I might be missing something.
Edit: It looks like SetConfigType is not for indicating the type of the configuration file, as in what extension, but rather how to parse the file.