Using localhost in composer was an extremely useful way to develop locally while seeing what interactives look like within guardian pages. Unfortunately composer only accepts HTTPS links now, which is a good thing but makes local dev'ing a bit more difficult.
Now to test from localhost you'll need to serve content over a secure connection which means self-signed certs. Here's a quick and dirty way to do that
1# Create a folder to store the keys
mkdir ~/ssl
2# Generate SSL keys. Enter a password for now, we'll get rid of it next then just skip over all the other questions
openssl req -x509 -newkey rsa:2048 -keyout ~/ssl/key.pem -out ~/ssl/cert.pem -days 999
3# Get rid of that password so it doesn't always ask for it
openssl rsa -in ~/ssl/key.pem -out ~/ssl/key.pem
4# Install / update the useful node http-server
sudo npm install http-server -g
5# Run the server in your interactive project folder
http-server --cors --ssl --cert ~/ssl/cert.pem --key ~/ssl/key.pem
6# You might want to alias that last command into something smaller by adding it to your ~/.bash_profile eg
echo 'alias webserver="http-server --ssl --cert ~/ssl/cert.pem --key ~/ssl/key.pem"' >> ~/.bash_profile
Enjoy.