Generate public and private keys

# private
openssl genpkey -algorithm RSA -out private.pem -pkeyopt rsa_keygen_bits:2048

# public
openssl rsa -pubout -in private.pem -out public.pem

Convert .pem keys to base64 string:

base64 -w 0 private.pem
base64 -w 0 public.pem

Pass base64 string to .env file:

JWT_PUBLIC_KEY=...
JWT_PRIVATE_KEY=...