This article will show you how to authenticate a user on an API.
Important Note:
You must first create and authenticate the API.
Who can use this feature?
System Administrator
Instructions
Log in to the site with your credentials
After you log in, type in /api after the domain's suffix
Example: civicplus.civicplus.com/api
In the site, enter your partition and apiKey fields:

Note: CivicPlus will provide these values.
For the UserToken, expand the Authentication tab:

Inside of Authentication, there are various API Calls.
Select the API /api/Authentication/v1/Authenticate:

Click on the Model Schema:

This will automatically populate the userCredentials value:

Replace the string value with the proper Username and Password:

Click Do It!:

This should generate an APIKey which will be the UserToken used above:

With the UserToken available, you can continue building your API Integration