I've set up my developer name and public key on WPEngine's Git Push dashboard. i'm able to connect via the terminal:
$ ssh git@git.wpengine.com info
hello <my wpengine dev name>
R W production/my_installname
R W staging/my_installname
so it all looks to be set up correctly.
but when trying to connect with Tower Git client, i'm getting the error:
Can't Authenticate with Server Authentication with the server failed. Please verify your username and password.
for the Tower login, i'm using:
Remote URL: git@git.wpengine.com:production/my_repo.git
Authentication: Private Key
Username: (i tried my dev name and my email address, neither worked)
SSH: ~/.ssh/id_rsa (which i generated for WPEngine, and uploaded the associated public key)
i've tried all different combinations of usernames and URLs, etc. nothing is working. any ideas? thank you!
From your question I gather you're on macOS, most likely macOS 10.12 which stopped autoloading SSH keys into the keychain and creating this situation. However, the Walkthrough is valid for all OS/Tower versions.
Navigate to Tower's service view with Cmd+Ctrl+S.
In the bottom left click the + to choose "Add Custom Server"
As authentication information enter
Server name: ssh://git@git.wpengine.com
Choose SSH Key authentication and enter your credentials
Should now work as expected
Open your repository in Tower, click your remote in the sidebar (most likely origin)
Hover the Fetch URL to reveal the "Edit" button
Press it and make sure your Custom Service is selected in this dialog
Test by clicking "Fetch"
You can find out more about connecting/authenticating the official Tower help:
https://www.git-tower.com/help/mac/manage-hosting-services/manage-ssh-keys
https://www.git-tower.com/help/mac/remote-repositories/connect-authenticate
Disclaimer: I'm with the support team for Tower