How to create HTTP header with Kafka header in SCDF httpclient (or http-request) app?

Question

I'm trying to create a test stream like this : time | oauth-processor | httpclient | log.

In this stream, my oauth-processor gets a token and store it in the kafka message headers. This one works well and I get a message like :

[
 payload=03/19/21 13:00:15, 
 headers={
  ... standard-headers ..., 
  ...
  OAuth={
    TokenType=bearer, 
    ExpiresIn=480, 
    AccessToken=myEncodedToken
  }
 }
]

Then I want to put the token in the HTTP header for authentication like this :

{
  'Content-Type':'application/json', 
  'Authorization':'bearer myEncodedToken'
}

Here is what I'm trying with the header-expression property in command line : --headers-expression={'Content-Type':'application/json', 'Authorization':#jsonPath(headers, \"$.OAuth.TokenType\").concat(\" \").concat(#jsonPath(headers, \"$.OAuth.AccessToken\"))}

but I can't manage to create a valid JSON string with SpEL.

The documentation for starter apps is very poor, as for SpEL in SCDF (especially when we have to escape characters) and I can't find anything helpful on the Internet

I would really appreciate any help. Thanks

Answer 1

I find a solution using a properties file with this line :

app.httpclient.headers-expression={'Content-Type':'application/json','Authorization' : headers.OAuth.Authorization}

SpEL is very confusing in SCDF...
Sometimes you need to use #jsonPath, sometimes not ...

Not sure but it seems that the comma was also breaking the expression in the command line