Custom Basecamp Identity Provider: Bread & Butter IO

Log in to the developer site of Basecamp:

Click Register one now to create your app.

For the name of your application, we recommend using your organization or company name.
Enter your company name, website, and logo.
Choose which Products apply to you.

Click on your app to open the App details.
Take note of the Client ID and Client Secret on the App page for the Bread & Butter setup below.

Go to https://app.breadbutter.io/sign-in/
Click Sign In and authenticate (or Sign Up make a new account and authenticate).
Go to Tools in the left menu.
Click on Basecamp under Social Accounts.
Select "Set Basecamp for Production".
Enter a custom name and description.
Enter the Client ID from the Basecamp setup steps above.
Enter the Client Secret from the Basecamp setup steps above.
Click Save & Close.
Click the checkbox next to your new Basecamp provider to enable it.