Most class files in MediaWiki OAuth extension are prefixed with MWOAuth prefix.
For example in the APISetup class, the file is named MWOAuthAPISetup.php. Now that MWOAuth prefix is no longer needed, the file needs to be renamed to APISetup.php.
This task is about hunting through the extension's files and removing all the occurrences of the prefix.
Extension repository: https://gerrit.wikimedia.org/g/mediawiki/extensions/OAuth
Learn more about Git, Gerrit and how to submit a patch: https://www.mediawiki.org/wiki/Gerrit/Tutorial