Double query parameter escaping around code

[mitar]

Describe the bug

I think this is a similar problem than what was already reported in #434, but elsewhere in the code. I believe all calls to url.QueryUnescape should be removed from the code. Go already escapes all query/form parameters automatically and unescaping again can just break things.

Example:

func GetRedirectURIFromRequestValues(values url.Values) (string, error) {
	// rfc6749 3.1.   Authorization Endpoint
	// The endpoint URI MAY include an "application/x-www-form-urlencoded" formatted (per Appendix B) query component
	redirectURI, err := url.QueryUnescape(values.Get("redirect_uri"))
	if err != nil {
		return "", errors.WithStack(ErrInvalidRequest.WithHint(`The "redirect_uri" parameter is malformed or missing.`).WithDebug(err.Error()))
	}
	return redirectURI, nil
}

[aeneasr]

If this is fixed, please add breaking tests first :)

[mitar]

Done in #480.