I would like to integrate signup of External Testflight users with an existing website we have that collects interested beta test users. I see that I can export any new signups once and a while and manually upload a CSV of their emails to testflight. This works somewhat well. But this is the digital age :) is there an API or tool like iTMSTransporter that will automate this process for me? Is everyone else just typing them in as they go or uploading CSV files once and a while?
You can launch an instance of boarding on heroku. It's part of the fastlane toolchain.