Service owner guides for how condition checks works and how to set up an endpoint

[SandGrainOne]

Description

Update documentation to include information about condition checks.

• How does it work
• The specification for an endpoint
• Scopes that Notifications will use to authenticate itself.

Tasks

• [ ] Write an article about how to set up an endpoint for a condition check.
• [x] Update existing guides to include the use of the condition property
• [x] Update the sales pitch for Notifications to include a note about condition checks.

Acceptance criteria

• [ ] Documentation gives clear instructions of the requirements of a condition check and how it works