AWS API Gateway Lambda Function with Cognito authentication returns 415 Unsupported Media Type

Question

UPDATE: I just noticed in the CloudWatch logs, that the content type has somehow mutated from application/json to text/plain. Here is what the WebHost string looks like now:

[Information] Microsoft.AspNetCore.Hosting.Internal.WebHost: Request starting POST https://snip.execute-api.us-west-2.amazonaws.com/Stage/api/Clinician text/plain

This is what it looked like when the call was working:

[Information] Microsoft.AspNetCore.Hosting.Internal.WebHost: Request starting POST https://snip.execute-api.us-west-2.amazonaws.com/Stage/api/Clinician application/json And yet, the header in Postman sets Content-Type: application/json

So why is the content type changing?

Beginning of original post:

I'm developing an API Gateway Lambda Function using Visual Studio 2017 "Serverless Application with Test" blueprint which is a .NET CORE solution. We are using Cognito User Pools for authentication. I am using Postman to test my first function. I'm passing a valid ID Token for a User in a Cognito User Pool. The request passes authentication but responds with a 415 Unsupported Media Type.

Before I started passing an ID Token, I was using AWS_IAM authorizer. At that time, the body (content-type: application/json) would map to the POST parameter successfully. But now that I am using the Cognito User Pool authorizer, I get a 415 Unsupported Media Type when calling POST. The POST method signature is:

    [HttpPost]
    public APIGatewayProxyResponse Post([FromBody]Clinician user)

The sample data I am sending in the body is:

{
"Id": "",
"Username": "6punk",
"Title": "Punker",
"FirstName": "Six",
"MIddleName": "",
"LastName": "Punk",
"Suffix": "",
"PreferredFirstName": "",
"PreferredLastName": "",
"Email": "[email protected]",
"Phone": "[phone]",
"UserSub": "",
"ClinicianTypeId": "1",
"EhrId": ""

}

As already mentioned, when authenticating as an IAM user or when testing via the Method Test pane in the API Gateway Console, the JSON maps perfectly to the Clinician class.

I have CORS enabled. For the ANY method, I have the Integration Request type set to LAMBDA_PROXY.

Any ideas what is causing the 415 Unsupported Media Type when testing my POST method from Postman with an ID Token from a Cognito User?

Answer 1

As it turns out, it was a bug in Postman. Even though I had specified the Content-type as application/json, it was passing the content type as text/plain. I deleted the Content-Type header and then recreated it and things started working. I had had Postman up for several days. I don't know for certain why it started passing text/plain. All I know is that when I deleted and recreated the Content-Type header as application/json, only then did things start working again.