Consume and validate JWT in Open Liberty - jwt

Question

I'm trying to use the jwt-1.0 feature in Open Liberty.
The JwtBuilder API is pretty nice and allows to set expiration, sign, encrypt and build a token programmatically (and everything else needed).
JwtBuilder.create().expirationTime(expTime).signWith(signAlg, privateKey).encryptWith(keyMgmtAlg, keyMgmtKey, contentEncAlg).buildJwt().compact();
But the JwtConsuer API seems pretty lame and only allows to read a token without validation at all.
JwtConsumer.create().createJwt(token);
Signature validation and decryption should be configured through the application server configuration (via "jwtConsumer" and "keystore" entries) but it's not possible programmatically.
I should accommodate with this but other validations like expiration date are not possible.
Do I miss something?

Answer 1

You're correct in that the JwtConsumer API does not provide a programmatic way to set specific validation requirements. However the JWT will still be validated when createJwt() is called.
The JwtConsumer API's create() and create(String consumerConfigId) methods tie the JwtConsumer object to a <jwtConsumer> element in the server configuration that specifies the validation requirements. The configuration settings for that element can be viewed here: https://openliberty.io/docs/22.0.0.4/reference/config/jwtConsumer.html.
The JwtConsumer.create() method will use the default <jwtConsumer> configuration that is provided automatically by the runtime, which simply looks like this:
<jwtConsumer id="defaultJwtConsumer" />
Similarly, the JwtConsumer.create(String consumerConfigId) would use the configuration with the corresponding ID. So JwtConsumer.create("myJwtConsumer") would use the corresponding "myJwtConsumer" configuration in the server.xml. That could look something like this:
<jwtConsumer id="myJwtConsumer"
issuer="https://example.com"
audiences="Luke, Leia, Han"
signatureAlgorithm="RS256"
jwkEnabled="true"
jwkEndpointUrl="https://..."
/>
You'd put whatever validation settings you want in that configuration. Then when you call JwtConsumer.createJwt(token), the runtime will perform several validation checks against the JWT. That includes checking the issuer, audiences, iat and exp times, the nbf claim, and of course the signature of the token.

Answer 2

To expand on the answer, if a clockSkew is not specified, then a default value of 5 minutes is used. On the other hand, setting clockSkew="0m" will in effect disable the clock skew.