Using Auth0 in your applications means that you will be "outsourcing" the authentication process to a centralized login page in the same way that Gmail, YouTube, and any other Google property redirects to accounts.google.com whenever a user signs in.
With machine-to-machine (M2M) apps, however, the system authenticates and authorizes the app rather than a user.
When your app needs to fetch user data from your API:
For M2M applications, Auth0 uses the Client Credentials Flow.
To implement the Client Credentials Flow, follow our Backend/API Quickstarts. The "Calling your API" section shows the required steps.
Or, to use our API endpoints, you can follow our tutorial: Call Your API Using the Client Credentials Flow.
Step-by-step instructions for tasks
Understand the fundamentals