$ mongosh --tls --tlsCertificateKeyFile /Users/abr/CAs/MongoDB-demo-CA/root/private/root.pem --tlsCAFile /Users/abr/CAs/MongoDB-demo-CA/root/certs/root.ca.crt.pem --host localhost --port 6578 --authenticationMechanism MONGODB-X509 --authenticationDatabase '$external' --username 'CN=MongoDB Admin,OU=Production MongoDB Clients,O=BK_man,ST=California,C=US' cg
Current sessionID:  cb6eeba50563528547c4d2d2
Enter password:
Connecting to:      mongodb://localhost:6578/cg
Using MongoDB:      4.4.0
Using Mongosh Beta: 0.4.0
For more information about mongosh, please see our docs: https://docs.mongodb.com/mongodb-shell/
> db.runCommand({connectionStatus:1})
{
  authInfo: {
    authenticatedUsers: [
      {
        user: 'CN=MongoDB Admin,OU=Production MongoDB Clients,O=BK_man,ST=California,C=US',
        db: '$external'
      }