gistfile1.txt

I can't comment, so I will put this as a separate answer. I found a few issues with the accepted one-liner answer:

The one-liner includes a passphrase in the key.
The one-liner uses SHA-1 which in many browsers throws warnings in console.
Here is a simplified version that removes the passphrase, ups the security to suppress warnings and includes a suggestion in comments to pass in -subj to remove the full question list:
```
openssl genrsa -out server.key 2048
openssl rsa -in server.key -out server.key
openssl req -sha256 -new -key server.key -out server.csr -subj '/CN=localhost'
openssl x509 -req -sha256 -days 365 -in server.csr -signkey server.key -out server.crt
```
Replace 'localhost' with whatever domain you require. You will need to run the first two commands one by one as OpenSSL will prompt for a passphrase.

To combine the two into a .pem file:
```
cat server.crt server.key > cert.pem
```