Fix CORS “Response to preflight…” header not present with AWS API gateway and amplify

Question

I\'ve been struggling so long with the error below. I\'ve tried so many tutorials and stackoverflow answers and none of the solutions fixes my problem.

Answer 1

So after a very helpfull discussion with @Jannes Botis I found the solution.

In template.yaml I changed my values to:

Globals:
  Function:
    Timeout: 10
  Api:
    Cors:
      AllowMethods: "'DELETE,GET,HEAD,OPTIONS,PATCH,POST,PUT'"
      AllowHeaders: "'Content-Type,X-Amz-Date,X-Amz-Security-Token,Authorization,X-Api-Key,X-Requested-With,Accept,Access-Control-Allow-Methods,Access-Control-Allow-Origin,Access-Control-Allow-Headers'"
      AllowOrigin: "'*'"

  MyAPIFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: myendpoint/
      Handler: app.lambdaHandler
      Runtime: nodejs12.x
      Events:
        GetMyData:
          Type: Api
          Properties:
            RestApiId: !Ref MyApi
            Path: /myendpoint
            Method: get
        Options:
          Type: Api
          Properties:
            RestApiId: !Ref MyApi
            Path: /myendpoint
            Method: options
            Auth:
              ApiKeyRequired: false

Note: You will get error "No 'xxx' header is present on the requested resource." where xxx is either Access-Control-Allow-Methods, Access-Control-Allow-Origin and Access-Control-Allow-Headers, thus you need to add them in your AllowHeaders. Also note that you have to add an Options resource with ApiKeyRequired: false.

Then your response from your options and get request should have the same headers:

headers: {
    "Access-Control-Allow-Headers": "Content-Type,X-Amz-Date,X-Amz-Security-Token,Authorization,X-Api-Key,X-Requested-With,Accept,Access-Control-Allow-Methods,Access-Control-Allow-Origin,Access-Control-Allow-Headers",
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "DELETE,GET,HEAD,OPTIONS,PATCH,POST,PUT",
    "X-Requested-With": "*"
}

Note: 'Accept' MUST BE PRESENT otherwise you will get "Response to preflight request doesn't pass access control check: It does not have HTTP ok status.".

Your preflight must be able to pass a 200 OK when you ommit the x-api-key in postman.