Wrong Base64 Encoding - Sourcetree Authentication failed if password contains special characters (§ and german umlauts)

We have the issue that some users are able to authenticate on Bitbucket Server using git or the weblogin, but not Sourcetree.

The error message is:

Authentication failed

Failed to check login for user [username] You do not have permission to access URL 'https://.../rest/api/1.0/users/username' please check the user credentials associated with this account. The request returned with status code 'Unauthorized'. Authentication failed. Please check your credentials and try again.

We changed the Bitbucket server back to http and checked the http-traffic.

There we see for the authentication a Base64-String containing username and password.

This is the case for git as well as for Sourcetree.

But when decoding the Sourcetree Base64-String you can see that certain characters are replaced by "?". So far this is the case for "§" as well as for german umlauts (ä,ö,ü).

As git is doing the correct encoding this seems to be a Bug in Sourcetree.

This happens with 3.4.1 as well as 3.4.6.

For us the workaround is to avoid these characters in the password.