Many publicly available APIs require the use of an API Key. The supplier of the API requests you to sign up and provide an email address or other contact information. In exchange for this, they provide an API Key, which activates the API.
The API Key is used to authenticate access. It may also be used to authorize specific features. Finally, it's also used to track usage. This may include throttling requests if an API Key is used too often in a given time period.
The variations in business models are numerous. For example, use of the API Key could be a billable event and charges are incurred. For other businesses, traffic must reach some threshold before payments are required.
What's important is non-repudiation of the use of the API. This, in turn, means creating API Keys that can act as a user's authentication credentials. The key must be difficult...
