Getting Access Token

[#1]

Hi. I'm new to working with Apache Nifi. Currently, I've Apache Nifi 2.3.0

I'm trying to get access_token so that I can use it in future API calls. Currently, I use Postman to test getting access_token value and it works. I want to do this via Nifi.

Here is what I setup Postman to get access_token

I'm currently using Postman in order to call an API that generates access_token that I will use later to call other APIs. I want to do the same using Apachi Nifi 2.3.0. The Apache Nifi should generate a file called tokens.txt that contains the access token. Here is what I do in Postman:

POST URL: https://URL/auth/token

Headers:

Content-Type: application/x-www-form-urlencoded;charset=UTF-8

Authorization: Basic <BASE_64_ENCODED_CLIENT_CREDENTIALS>

Body:

grant_type: client_credentials

The response is in JSON format and contains the access token, expiration time of the access token.
Here is an example response:
{
"access_token": "eyJ4NXQjUzI1NiI...KtK5elB38rcAbgFtVP9A",
"token_type": "Bearer",
"expires_in": 3600
}

What do I need to achieve?

I want to simulate the above in Apache Nifi where I get the access_token and then store it in a file. Every time a new access token arrives, it needs to re-write the value.

I tried to use the following components

GenerateFlowFile -> EncodeContent -> UpdateAttribute (headers and body) -> InvokeHTTP -> LogAttribute (API-Response) -> EvaluateJsonPath -> UpdateAttribute (filename) -> PutFile

But for some reason, the InvokeHTTP was not working (not getting the response in JSON format).

[#2]

@BuffaloDaddy Welcome to the Cloudera Community!

To help you get the best possible solution, I have tagged our NiFi experts @MattWho @SAMSAL @Shelton  who may be able to assist you further.

Please keep us updated on your post, and we hope you find a satisfactory solution to your query.

[#3]

Thanks @DianaTorres . So, let me give more details about my issue. Below is how my process group look like:

1) GenerateFlowFile Processor: I define there the attributes that I want to pass in InvokeHTTP processor. This includes:

• Authorization
• content-type
• grant_type

2) LogAttribute-BeforeINVOKE: This processor is to log attributes in Logfile before HTTPInvoke

3) InvokeHTTP: This processor is where I make API call to get access_token. (Screenshots below). I've the property Request Body Enabled set as true.

4) LogAttribute-AFTERINVOKE: This processor is to log attributes in Logfile after HTTPInvoke

My observations: 

• If I make the request using curl "e.g. curl -X POST https://SERVER_NAME/auth/token -H "Content-Type: application/x-www-form-urlencoded;charset=UTF-8" -H "authorization: Basic CLIENT_SECRET_VALUE" -d "grant_type=client_credentials", I get access_token.
• I'm suspecting that InvokeHTTP processor when sending the request, some of the parameters might be not parsed properly because of special characters in content-type or authorization.

I hope that  @MattWho or @SAMSAL or @Shelton can help me with this. It's driving me crazy.

Attributes of InvokeHTTP (SEND)

Attributes of InvokeHTTP (ATTRIBUTES_MODIFIED)