Using predictable/constant cryptographic key when creating and verifing Json Web Token.

[KANIXB]

Hi, we are a research group to help developers build secure applications. We designed a cryptographic misuse detector on Java language(Our main concern is the secure implementation and use of Json Web Token). We found your great public repository (i.e.,
microservice-integration)from Github, and several security issues detected by our detector are shown in the following. The specific security issues we found are as follows:
(1) Location: Package: com.blueskykong.auth.config.oauth; Class: OAuth2Config.class Method: JwtAccessTokenConverter
Security issue: Using predictable/constant cryptographic key when creating and verifing Json Web Token. (The key is hard-coded and not have enough strength. It is suggest the length of HMAC key is as long as the length of the output. )

Using a predictable/constant secret does not conform to the security implementation specification of JWT, which may bring security risks to your system. It is recommended to use a more secure way to store the secret used to generate the JWT and use a strong enough key to improve the security of the project. （For the hazards of predictable/constant secret, you can refer to CWE-321, NIST Special Publication 800-57).

We wish the above security issues cloud truly help you to build a secure application. If you have any concern or suggestion, please feel free to contact us, we are looking forward to your reply. Thanks.