How to generate cert for test use

version
{
"azure-cli": "2.31.0",
"azure-cli-core": "2.31.0",
"azure-cli-telemetry": "1.0.6"
}

**Describe the bug**
I follow the doc https://docs.microsoft.com/en-us/azure/active-directory/develop/howto-create-service-principal-portal to generate a certificate for service principal. I only can export cer and pfx from ```certmgr```. And I upload the cer to the service principal. Because ```az-cli``` does not support pfx to login service principal. So I use ```openssl pkcs12 -in 2.pfx -out 3.pem -nodes``` to convert pfx to pem. But when I login by using this pem, I get error as below.
AADSTS7000215: Invalid client secret is provided.
Trace ID: f0ac8dc9-8841-4a44-a9a3-2882efa90600
Correlation ID: 31d07a43-b82b-4f49-a2ef-e05245d1dc68

Do you have any idea about how to generate certificate for self test?