fix: ensure SQL processor uses key returned by query

[ncc-akis]

This PR addresses two issues in the SQL KID processor which prevent it being exploitable in the intended fashion.

1. The code following the SQL query assumes a single result returned by the query, while the execute method uses the default "all" method which returns a list of results. This has been modified to use the "get" method which will return a single result.
2. After the query has been executed, the key used is still always the default key, rather than the one returned by a query. This means that the JWT will only be validated if signed using the default key rather than an attacker-specified key. This has been modified to always use the key returned by the query, allowing the attacker to control the key used to sign the token.

[pmstss]

Thank you for your contribution! The changes make sense to me.

✅ LGTM