What do you exactly mean with: "Please check if you have obtained the API key for your custom API" ?? I followed this toturial to create the Azure function api: https://docs.microsoft.com/en-gb/azure/azure-functions/functions-openapi-definition
Do you mean this step in the tutorial? 
Also my api definition template is created like in the tutorial. You see below in the template the authentication type.
{
"swagger": "2.0",
"info": {
"title": "myCompany.azurewebsites.net",
"version": "1.0.0"
},
"host": "myCompany.azurewebsites.net",
"basePath": "/",
"schemes": [ "https", "http" ],
"paths": {
"/api/TurbineRepair": {
"post": {
"operationId": "CalculateCosts",
"description": "Determines if a technician should be sent for repair",
"summary": "Calculates costs",
"x-ms-summary": "Calculates costs",
"x-ms-visibility": "important",
"produces": [ "application/json" ],
"consumes": [ "application/json" ],
"parameters": [
{
"name": "body",
"in": "body",
"description": "Hours and capacity used to calculate costs",
"x-ms-summary": "Hours and capacity",
"x-ms-visibility": "important",
"required": true,
"schema": {
"type": "object",
"properties": {
"hours": {
"description": "The amount of effort in hours required to conduct repair",
"type": "number",
"x-ms-summary": "Hours",
"x-ms-visibility": "important"
},
"capacity": {
"description": "The max output of a turbine in kilowatts",
"type": "number",
"x-ms-summary": "Capacity",
"x-ms-visibility": "important"
}
}
}
}
],
"responses": {
"200": {
"description": "Message with cost and revenue numbers",
"x-ms-summary": "Message",
"schema": {
"type": "object",
"properties": {
"message": {
"type": "string",
"description": "Returns Yes or No depending on calculations",
"x-ms-summary": "Message"
},
"revenueOpportunity": {
"type": "string",
"description": "The revenue opportunity cost",
"x-ms-summary": "RevenueOpportunity"
},
"costToFix": {
"type": "string",
"description": "The cost in $ to fix the turbine",
"x-ms-summary": "CostToFix"
}
}
}
}
},
"security": [ { "apikeyQuery": [] } ]
}
}
},
"definitions": {},
"securityDefinitions": {
"apikeyQuery": {
"type": "apiKey",
"name": "code",
"in": "query"
}
}
}
