Amazon web service- API Gate way - Custom authorizer using lambda function issue

Question

I have a scenario where the caller of my services is going to pass a JWT (JSON web token), and I want to pass that value to a custom authorizer that uses lambda function in order to decrypt it and return a policy to that caller where the policy can be allow that user or deny it. in addtion of adding a header value after the lambda completes the JWT decryption.

for Example:

The caller (end user) call a service serviceX(POST/Get).
call reaches AWS API GateWay
Service is marked with authorised method which is custom authorizer
Custom Authorizer calls lambda function
Lambda function decrypt the JWT
Lambda function adds a new header/modify an existing one
end service (serviceX) receives the request

I have implemented all the above example except number 6, I can't add a new header value from lambda or modify an existing one.

I have searched a lot and I can't find a way to do so.

any further documentation or snippets from AWS about this issue I will provide it by request -if needed-.

What are you using as an integration? HTTP, Lambda, another AWS service? — Bob Kinney
– Bob Kinney, Commented Jan 30, 2017 at 17:47

doorstuck · Accepted Answer · 2017-01-31 11:15:26Z

1

You cannot set a header from the custom authorizer. You can however return a context map of values that you can use in the serviceX function.

So the custom authorizer returns the policy together with a context:

{
    "principalId": "yyyyyyyy",
    "policyDocument": {
        ... blah blah ...
    },
    "context": {
        "customvalue": "response-from-number-6"
    }
}

Then you can access it in the serviceX function in the the following attribute:

$context.authorizer.customvalue

Does that solve your number 6 of returning a value from the custom authorizer?

answered Jan 31, 2017 at 11:15

doorstuck

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2 Comments

majd 7yari Over a year ago

are you referring to use the customvalue in the serviceX payload/body ? and I have used this senior to set the customvalue in the serviceX payload, but i need to use this customvalue to add it in the request header. do you have any ideas how to implement this ?

jackko Over a year ago

You can use the same syntax $context.authorizer.customvalue to set the value for a request header to serviceX

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