eBay uses unique identifiers called “application keysets” that tell eBay which application is making a call. The application keyset serves as your application’s credentials.
Application ID/client ID—Uniquely identifies your application; can’t be changed
Dev ID—Uniquely identifies your developer profile; can’t be changed
Cert ID/secret—A client secret, like a password for this keyset, that should be kept confidential; can be reset
You can create a separate keyset for the Sandbox and Production environments.
Tip: Just as you would store and protect passwords, use the same caution in storing and using your application keyset. For example, if authorization strings are hard-coded in a compiled application, an unethical individual could see the IDs by inspecting or reverse engineering. We highly recommend using strong encryption of the IDs in your application to prevent credential theft.