I am integrating Bitbucket with Netlify and Netlify CMS, which uses client side implicit grant to log in and make changes in the repo.
I have set up an OAuth consumer on Bitbucket and have added the Netlify callback URL [ https://api.netlify.com/auth/done ]and the necessary write access to Account and Repositories.
I then added the resulting Bitbucket OAuth key and secret to Netlify settings. I also did the CMS setup.

However, when I then try to log in to the CMS through Bitbucket, I get the error message:
Invalid redirect_uri
This integration is misconfigured. Contact the vendor for assistance.

I saw that on June 5, there was a problem which resulted in this error, but it seems to have been resolved.