API List visible roles for a user for a unit

[franck-boullier]

How it should work:

• 3rd party app calls an endpoint

Input:

• User API key: the API key for the user
• MEFE unit ID: the mefe unit Id for the unit.

Response:

List of all the roles that the user is allowed to see for this unit.

Why this is important:

This is needed so that it's possible to create a case without returning error.