Please add better error message for when a DID tries to issue a credential to itself

[barrybecker4]

Expected behaviour

I would have been able to debug my problem much faster if the error message was
{
"message": "The DID in the request cannot be the same as the credentialSubject. In other words, you cannot issue a credential to yourself."
}

The problem is that you cannot have the DID in the request URL be the same as the DID in the credentialSubject.
IOW, you cannot issue a credential to yourself. I guess that makes sense, but the message could be clearer. I will issue a feature request for that.

Actual behaviour

Instead, I was stuck for a long time trying to understand what
{
"message": "cannot parse claim"
}
meant. Even after reading this, I was not sure. It took some experimenting in postman before I realized what was going on.

Steps to reproduce the problem

Try to issue a credential to the issuer.

System information

Issuer node version: v2.X.X (how to tell the version?)
OS & Version: Linux
Browser & Version: Chrome/Firefox/Safari/Edge