Custom Dropbox Identity Provider: Bread & Butter IO

Log in to the developer site of Dropbox:

Click on App Console at the top right, then Create app.

Choose Scoped access for your app's API.
Choose App Folder for the type of access you need.
Enter your App Name. For App Name, we recommend using your organization or company name.
Click Create app.

Go to the Settings tab.
For the Redirect URIs in the OAuth 2 section, enter:

https://api.breadbutter.io/callback
Click Add.

On the Settings page, click Apply for production.
Follow the steps to complete the production application process. This is required in order for users to authenticate with your App using Dropbox.

Take note of the Client ID and Client Secret (called App Key and App 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 Settings in the left menu.
Click on Dropbox under SSO Settings > Social Accounts.
Select "Set Dropbox for Production".
Enter a custom name and description.
Enter the Client ID from the Dropbox setup steps above.
Enter the Client Secret from the Dropbox setup steps above.
Click Save.
Click the checkbox next to your new Dropbox provider to enable it.