Following @comxd's #6 (comment)
In my case (MantisBT 2.10) the htaccess located at /plugins folder prevent access to the plugin.js file located at /plugins/GoogleOauth/pages/assets/js/plugin.js
This is due to incorrectly referencing the javascript file via direct URL [1] instead of leveraging the plugin API. For an example of how it should be done, please see Snippets plugin.
Following @comxd's #6 (comment)
This is due to incorrectly referencing the javascript file via direct URL [1] instead of leveraging the plugin API. For an example of how it should be done, please see Snippets plugin.