title: Encoding of security.oauth2.resource.jwt.key-value
body: <p>I use Spring Boot with the spring-security-oauth2 module to build a RESTful API.
  I also have an (external) auth server delivering JWT, and a secret key to verify the signature (<code>security.oauth2.resource.jwt.key-value</code>); the algorithm is HMAC.</p>
  
  <p>The problem is that the key is base 64 url encoded, and as far as I understand reading the source code, the property <code>security.oauth2.resource.jwt.key-value</code> must be plain text.</p>
  
  <p>I tried to manually decode the key and set it in the external configuration file, but this doesn't work.</p>
  
  <p>So the question is: what can I do? Is there a way to decode it on the fly before the beans are configured? Another suggestions?</p>
  
  <p>Thanks in advance.</p>