# on 0.5.x
dokku plugin:install https://github.com/dokku/dokku-global-cert.git  global-cert

# first create the global certificate directory:
mkdir -p /var/lib/dokku/config/global-cert/

# now copy your cert and key into this directory
cp ssl.crt /var/lib/dokku/config/global-cert/ssl.crt
cp ssl.key /var/lib/dokku/config/global-cert/ssl.key

# and now all applications being deployed will have
# the global certificate automatically set