AWS API Gateway - URL rewrite

Question

My requirement is to rewrite url in API Gateway  (REST API) . 
API Gateway (+ Lambda authorizer) --> VPC Link --> NLB--> (internal) ALB -->  ECS
For e.g. if my external facing url is "bookings/trains/7010"
it needs to be rewritten as "bookings/clients/123/trains/7010" when calling backend url  where I extract clients data from the encrypted token (during auth token validation) in Lambda authorizer.
Is there way to do it in gateway?

Accepted Answer

For an API Gateway operation like this:  
```
/bookings/trains/{trainID}
```

Calling a backend API like this: 
```
/bookings/clients/{clientID}/trains/{trainID}
```

The trainID Path Parameter, "7010", will map straight across to the Endpoint URL defined in your API Integration Request.

To get the clientID from your Lambda Custom Authorizer, you would need to make sure the authorizer returns the following context map:

```
"context" : {
  "clientID": "123"
}
```

Then implement a Request Mapping Template with the following line of code:

```
#set($context.requestOverride.path.clientID = $context.authorizer.clientID)
```

AWS API Gateway - URL rewrite

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