@Override
    public String toString() {
        final StringBuilder buffer = new StringBuilder();
        buffer.append(schemeName).append(" ");
        if (value != null) {
            buffer.append(value);
        } else if (params != null) {
            buffer.append(params);
        }
        return buffer.toString();
    }
This class represents an authentication challenge consisting of a auth scheme
and either a single parameter or a list of name / value pairs.

@since 5.0
httpclient5/src/main/java/org/apache/hc/client5/http/auth/AuthChallenge.java