How do you do AWS Lambda function with Function URL Authentication with postman?

Question

I have a lambda function that I've been working on and testing with Postman using an HTTP function URL. Now I have applied the Function URL Auth Type "AWS_IAM".

I've created a user with "Access key - Programmatic access" and the AWSLambdaRole which in the permissions json, applies Action: "lambda:InvokeFunction". I have the access key and secret key for this user.

In postman I have selected "AWS Signature" for auth type, and I have entered the access key and secret key. I've also entered my AWS Region. However, I don't know what to enter for "Service Name". The only examples I can find are for accessing APIs created with API Gateway, so the service name indicated is "execute-api". I'm guessing that is not correct for hitting a lambda Function URL. Either that, or I'm doing something else wrong.

the response is always: {"Message":"Forbidden"}

What should the service name be for accessing a Lambda Function URl with AWS_IAM Auth Type?

I've spent a lot of time searching and can't find an example demonstrating this.

Answer 1

The IAM permission required to invoke a Lambda function in AWS is:

Action: "lambda:InvokeFunction"
Resource: <ARN of Lambda function>

But IAM permission to invoke a Lambda function URL is different. It's:

Action: "lambda:InvokeFunctionUrl"
Resource: <ARN of Lambda function>

You would give these permissions to an IAM principal when using the AWS_IAM auth type for function URLs. See Security and auth model for Lambda function URLs for more.