Keycat is a easy authenticator created by the EOSDAQ team. It can be easily integrated into dApps in any blockchain. It runs on Safari, Chrome, and Firefox, both desktop or mobile. Read more about Keycat on their website.
Click Import Account if you've never setup Keycat before. It will take you to the follow screen below, where you enter your Account (your EOS username) and a field to enter your Private Key. Click Next when completed.
You must select "Save" to use the one-click login function continuously in the future.
You should see your account username in the top right corner if you have successfully logged in.