I need to make a secure HTTP callout from Salesforce (using Apex) to AWS Lambda and I build my first version using AWS API Gateway. I realized I can get a client certificate from API Gateway (.crt) but this looks like it is only for AWS backend and is not meant to be for the HTTP request sent to API Gateway. What are my alternatives to establish a secure connection from outside AWS (Salesforce) to a Lambda function?
So far I've found this, which is a disappointing dead-end for now.