I am using WordPress on my live server which only uses SFTP using an SSH key.
I want to install and upgrade plugins, but it appears that you are required to enter your FTP login to install the plugins. Is there a way to install and upgrade plugins by manually uploading the files instead of having WordPress handle the entire process?
As stated before none of the perm fixes work anymore. You need to change the perms accordingly AND put the following in your wp-config.php:
define('FS_METHOD', 'direct');
I also recommend the SSH SFTP Updater Support plugin. Just solved all my problems too...especially in regards to getting plugins to delete through the admin. Just install it in the usual way, and the next time you're prompted by WordPress for FTP details, there'll be extra fields for you to copy/paste your private SSH key or upload your PEM file.
Only problem I have is in getting it to remember the key (tried both methods). Don't like the idea of having to find and enter it every time I need to delete a plugin. But at least it's a solid fix for now.