Recently working with an Azure Functions , we had to define its REST Signature using Swagger to be able to use it within PowerApps.
The Azure Function expected the code query parameter basically the apiKey for the function and JSON Body with custom object named Lead having following properties as POST method.
This is how we’d define our Lead Object and pass it as one of the parameters in the body.
swagger: '2.0' info: title: mycrmfunctionapp.azurewebsites.net version: 1.0.0 host: mycrmfunctionapp.azurewebsites.net basePath: / schemes: - https - http paths: /api/MyLeadWebHook: post: operationId: /api/MyLeadWebHook/post produces: - application/json consumes: - application/json parameters: - name: Lead in: body description: lead object required: true schema: $ref: '#/definitions/Lead' description: >- Replace with Operation Object #http://swagger.io/specification/#operationObject responses: '200': description: Success operation security: - apikeyQuery:  definitions: Lead: description: Lead Object properties: fullname: type: string description: full name topic: type: string description: topic email: type: string description: topic required: - fullname - topic - email securityDefinitions: apikeyQuery: type: apiKey name: code in: query
Hope it helps..