Add Test Case for KID Injection

[Merenon]

4.1.4. "kid" (Key ID) Header Parameter
The "kid" (key ID) Header Parameter is a hint indicating which key
was used to secure the JWS. This parameter allows originators to
explicitly signal a change of key to recipients. The structure of
the "kid" value is unspecified. Its value MUST be a case-sensitive
string. Use of this Header Parameter is OPTIONAL.
When used with a JWK, the "kid" value is used to match a JWK "kid"
parameter value.

The KID value might be used to retrieve the key from a database or the file system and might be vulnerable to injections.