If you are a Heroku user using the SendGrid Add-on, and would like to access the SendGrid web interface, you can find your SendGrid credentials by issuing the following command:

heroku config --long

You can also go the other direction and configure heroku to use an existing SendGrid account and password. Just run the following commands from your shell: 

heroku config:add SENDGRID_USERNAME=existing_username 
heroku config:add SENDGRID_PASSWORD=existing_password 
heroku restart 

Make sure that your SENDGRID_DOMAIN config var matches the website field in your SendGrid profile.