public OAuth2TokenDescriptorBuilder issuer(String issuer) {
        this.issuer = requireNonNull(issuer, "issuer");
        return this;
    }
{@code iss} Token Introspection Response field,
OPTIONAL. String representing the issuer of this token, as defined at
<a href="https://datatracker.ietf.org/doc/rfc7519/">[RFC7519]</a>.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/OAuth2TokenDescriptorBuilder.java