Validate Cognito tokens in Kong

Assuming Kong environment is set up and operating as expected, this blog helps to Validate Cognito tokens in Kong. 

 JWT token issued by popular identity solutions such as Auth0, Amazon Cognito etc., can be easily Authorized by kong.  Here are the steps to validate JWT token issued by Auth0 in Kong.  In this blog, I am going to focus on how to validate JWT token issued by Amazon Cognito. 

Assuming that Amazon Cognito user pools are set up and operating as expected.  Every successful authentication of a user, Amazon Cognito issues 
  • ID Token
  • Access Token
ID token is represented as a JSON Web Key Token (JWT). The token contains claims about the identity of the authenticated user. For example, it includes claims such as name, family_name, phone_number, etc., For more information about standard claims, see the OpenID Connect specification.

 Extract the public key from Amazon Cognito public endpoint using  

 https://cognito-idp.{region}.amazonaws.com/{userPoolId}/.well-known/jwks.json

 Using library convert jwks to pem, save as cognito_public_key.pem

1. Create an endpoint in kong

 curl -i -X POST http://localhost:8001/apis \ --data "name={api}" \ --data "hosts=example.com" \ --data "upstream_url=http://httpbin.org"

 2. Enable it with JWT

 curl -X POST http://localhost:8001/apis/{api}/plugins \ --data "name=jwt" --data "config.claims_to_verify=exp"

3. Create a consumer

 curl -i -X POST http://kong:8001/consumers \ --data "username=<USERNAME>" \ --data "custom_id=<CUSTOM_ID>"

 4. Apply cognito public key to the consumer to validate JWT tokens

 curl -i -X POST http://localhost:8001/consumers/{consumer}/jwt \ -F "algorithm=RS256" \ -F "rsa_public_key=@./cognito_public_key.pem" \ -F "key=https://cognito-idp.{region}.amazonaws.com/{userPoolId}"

5. Finally, test the endpoint 

 curl -i http://localhost:8000 \ -H "Host:example.com" \ -H "Authorization:Bearer <JWT_Token>"
Location: Melbourne VIC, Australia

Comments

Unknown said…
This comment has been removed by the author.
March 17, 2018 at 1:12 PM
Unknown said…
Very useful article Senthil - thanks.

I have one question:
It seems to me that each AWS cognito pool is associated with two different pairs of keys (not sure why, but this KB article alludes to it)
https://aws.amazon.com/premiumsupport/knowledge-center/decode-verify-cognito-json-token/

Now, I understand that a JWT token header contains a key id (kid), so the association with a particular public key is possible, but is this association between key id and public key performed automatically by the kong JWT plugin?

If not, I am not sure how the token signature could be verified.


April 20, 2018 at 7:51 AM
Senthil said…
Hi Steve, thanks for visiting my blog.

Amazon Cognito generates two pairs of RSA keys for each user pool. One of the private keys is used to sign the token. To verify the signature of an Amazon Cognito JWT, first search for the key with a key ID that matches the key ID of the JWT. Then, use libraries to decode the token and verify the signature.

Refer the following for better understanding,
https://aws.amazon.com/premiumsupport/knowledge-center/decode-verify-cognito-json-token/
https://github.com/awslabs/aws-support-tools/tree/master/Cognito/decode-verify-jwt
April 24, 2018 at 5:15 AM
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