Even though providing a Certificate Authority is required, no attempts are made to enforce it is still valid.
openssl genrsa -out CAPCA.key 2048 openssl req -x509 -new -nodes -key CAPCA.key -out CAPCA.pem -subj "/C=US/ST=California/OU=CAPRoot/L=Palo Alto/CN=127.0.0.1" -days -1 openssl req -new -newkey rsa:1024 -nodes -out Bongo.req -keyout Bongo.key -subj "/C=US/ST=California/OU=CAP/L=Palo Alto/CN=127.0.0.1" -days 2 openssl x509 -CA CAPCA.pem -CAkey CAPCA.key -CAcreateserial -req -in Bongo.req -out Bongo.pem -days 2 cat Bongo.key Bongo.pem > combined.pem mongod --sslMode requireSSL --sslPEMKeyFile combined.pem --sslCAFile CAPCA.pem --smallfiles --dbpath /tmp --port 2000