You can find your Akamai (Linode) API keys within the Akamai Cloud control panel. Head to cloud.linode.com, create an account (if you don't already have one) and login.
In the top right corner of the page, click the down arrow next to your username and find the "API Tokens" link in the drop down menu, under the "My Profile" heading.
Click the button to "Create a Personal Access Token", a modal window should appear. Give the token a label like "ServerAuth API" so you know what the token is for, set an expiration time and make sure Read/Write permissions are set for all options and click "Create Token".
A new modal window will appear with the token, which should look similar to
Copy this and save it to your Akamai server provider within ServerAuth.
NOTE: When setting the expiration time, best practises dictate that you should set an expiration and refresh the token every few months to prevent unwanted access. However, please be aware that in doing so ServerAuth may not be able to access your Akamai account and may not be able to perform all the actions required.