java.lang.IllegalArgumentException: secret key byte array cannot be null or empty

Question

I am using spring-boot with JWT.

Application.properties

jwt.secret=xyz

Controller.java

@PostMapping(path = "/authenticate")
    public ResponseEntity<?> createAuthenticationToken(@RequestBody JwtRequest authenticationRequest) throws Exception {

        authenticate(authenticationRequest.getUsername(), authenticationRequest.getPassword());

        final UserDetails userDetails = userDetailsService.loadUserByUsername(authenticationRequest.getUsername());

        final String token = jwtTokenUtil.generateToken(userDetails);

        return ResponseEntity.ok(new JwtResponse(token));
    }

JwtTokenUtil.java

    @Value("${jwt.secret}")
    private String secret;
    public String generateToken(UserDetails userDetails) {
            Map<String, Object> claims = new HashMap<>();
            return doGenerateToken(claims, userDetails.getUsername());
        }

        private String doGenerateToken(Map<String, Object> claims, String subject) {

            return Jwts.builder().setClaims(claims).setSubject(subject).setIssuedAt(new Date(System.currentTimeMillis()))
                    .setExpiration(new Date(System.currentTimeMillis() + JWT_TOKEN_VALIDITY*1000)).signWith(SignatureAlgorithm.HS512, secret).compact();
        }

in the jwtTokenUtil.generateToken code I am getting the following error

ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.IllegalArgumentException: secret key byte array cannot be null or empty.] with root cause
java.lang.IllegalArgumentException: secret key byte array cannot be null or empty.
    at io.jsonwebtoken.lang.Assert.notEmpty(Assert.java:204)
    at io.jsonwebtoken.impl.DefaultJwtBuilder.signWith(DefaultJwtBuilder.java:88)
    at io.jsonwebtoken.impl.DefaultJwtBuilder.signWith(DefaultJwtBuilder.java:100)
    at net.javaguides.springboot.helloworldapp.config.JwtTokenUtil.doGenerateToken(JwtTokenUtil.java:66)
    at net.javaguides.springboot.helloworldapp.config.JwtTokenUtil.generateToken(JwtTokenUtil.java:60)
    at net.javaguides.springboot.helloworldapp.controller.BasicAuthController.createAuthenticationToken(BasicAuthController.java:75)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800)

When I have given my credentials I am getting this error. the application is already validated my credentials, but while generating the token I am getting this error.

UPDATE:-

While debugging I have seen the internal code like below

 @Override
    public JwtBuilder signWith(SignatureAlgorithm alg, String base64EncodedSecretKey) {
        Assert.hasText(base64EncodedSecretKey, "base64-encoded secret key cannot be null or empty.");
        Assert.isTrue(alg.isHmac(), "Base64-encoded key bytes may only be specified for HMAC signatures.  If using RSA or Elliptic Curve, use the signWith(SignatureAlgorithm, Key) method instead.");
        byte[] bytes = TextCodec.BASE64.decode(base64EncodedSecretKey);
        return signWith(alg, bytes);
    }

In this bytes I am getting null

Answer 1

I think your key need to be base64 encoded See Source: https://github.com/jwtk/jjwt/blob/master/impl/src/main/java/io/jsonwebtoken/impl/DefaultJwtBuilder.java#L138

Try following:

    private String doGenerateToken(Map<String, Object> claims, String subject) {

String encodedString = Base64.getEncoder().encodeToString(secret.getBytes())
        return Jwts.builder().setClaims(claims).setSubject(subject).setIssuedAt(new Date(System.currentTimeMillis()))
                .setExpiration(new Date(System.currentTimeMillis() + JWT_TOKEN_VALIDITY*1000)).signWith(SignatureAlgorithm.HS512, encodedString ).compact();
    }

Answer 2

The secret key is too short. I had the same error and just changing from

jwt.secret=omg

to

jwt.secret=HRlELXqpSB

solved the issue.