public OAuth2AuthorizationGrant build() {
        checkState(requestSupplier != null, "accessTokenRequest() is not set.");
        return new DefaultOAuth2AuthorizationGrant(
                accessTokenEndpoint, accessTokenEndpointPath, requestSupplier, responseHandler, refreshBefore,
                fallbackTokenProvider, newTokenConsumer);
    }
Returns a newly created {@link OAuth2AuthorizationGrant} based on the configuration set so far.
oauth2/src/main/java/com/linecorp/armeria/client/auth/oauth2/OAuth2AuthorizationGrantBuilder.java