Spring Cloud Gateway altering form data does not work - reactive-programming

Question

I defined this GatewayFilter:
EDIT More context information:
What I would like to achieve is to avoid the client providing its credentials to get an access token from an authorization server.
The client sends a POST request with user's credentials (username/password) and the gateway adds all complementary information like scope, client_id, grant_type etc... before forwarding the request to the authorization server.
#Component
public class OAuth2CredentialsAppenderGatewayFilterFactory extends AbstractGatewayFilterFactory<OAuth2CredentialsAppenderGatewayFilterFactory.Config> {
public OAuth2CredentialsAppenderGatewayFilterFactory() {
super(Config.class);
}
#Override
public GatewayFilter apply(Config config) {
return (exchange, chain) -> {
ServerHttpRequest request = exchange.getRequest();
ServerHttpRequest.Builder requestBuilder = exchange.getRequest().mutate();
if ("x-www-form-urlencoded".equals(request.getHeaders().getContentType().getSubtype())) {
//This code is not executed, the call of formData.put does not do anything, even a breakpoint is not reached!
if (request.getMethod().equals(HttpMethod.POST)) {
exchange.getFormData().map(formData -> {
formData.put("key1", List.of("value1"));
formData.put("key2", List.of("value2"));
formData.put("key3", List.of("value3"));
return formData;
});
}
//This part of code works well, the header is added to the forwarded request
requestBuilder.header(HttpHeaders.AUTHORIZATION,
"Basic " + Base64Utils.encodeToString((this.uiClientId + ":" + this.uiClientSecret).getBytes()));
}
return chain.filter(exchange.mutate().request(requestBuilder.build()).build());
};
}
}
I use the filter like this:
- id: keycloak_token_route
uri: http://localhost:8180
predicates:
- Path=/kc/token
filters:
- OAuth2CredentialsAppender
- SetPath=/auth/realms/main/protocol/openid-connect/token
- name: RequestRateLimiter
args:
key-resolver: "#{#userIpKeyResolver}"
redis-rate-limiter.replenishRate: 20
redis-rate-limiter.burstCapacity: 30
denyEmptyKey: false
The filter is well invoked but altering the incoming request body does not work.
I am new to the reactive world so I am a bit confused, any help will be appreciated.

Answer 1

For those who would like to do the same thing, this is how I solved my problem. Again I am not an expert of Reactive programming, I am still learning it so it might be a better answer.
#Component
public class OAuth2CredentialsAppenderGatewayFilterFactory extends AbstractGatewayFilterFactory<OAuth2CredentialsAppenderGatewayFilterFactory.Config> {
#Value("${uiservice.clientId}")
private String uiClientId;
#Value("${uiservice.clientSecret}")
private String uiClientSecret;
public OAuth2CredentialsAppenderGatewayFilterFactory() {
super(Config.class);
}
#Override
public GatewayFilter apply(Config config) {
return (ServerWebExchange exchange, GatewayFilterChain chain) -> {
ServerHttpRequest request = exchange.getRequest();
ServerHttpRequest.Builder requestBuilder = exchange.getRequest().mutate();
if (nonNull(request.getHeaders().getContentType()) && request.getHeaders().getContentType().equals(MediaType.APPLICATION_FORM_URLENCODED)) {
if (requireNonNull(request.getMethod()).equals(HttpMethod.POST)) {
//Use this filter to modify the request body
ModifyRequestBodyGatewayFilterFactory.Config requestConf = new ModifyRequestBodyGatewayFilterFactory.Config()
.setContentType(MediaType.APPLICATION_FORM_URLENCODED_VALUE)
.setRewriteFunction(String.class, String.class, this.completeRequestBody());
requestBuilder.header(HttpHeaders.AUTHORIZATION, base64Encoding(this.uiClientId, this.uiClientSecret));
return new ModifyRequestBodyGatewayFilterFactory().apply(requestConf).filter(exchange.mutate().request(requestBuilder.build()).build(), chain);
}
}
return chain.filter(exchange.mutate().request(requestBuilder.build()).build());
};
}
/** Add some config params if needed */
public static class Config {
}
/** Complete request by adding required information to get the access token. Here we can get 2 type of token: client_credentials or password. If the param client_only=true we should get a client_credentials token */
private RewriteFunction<String, String> completeRequestBody() {
return (ServerWebExchange ex, String requestBody) -> {
requireNonNull(requestBody, "Body is required");
//if body contains only this, we should get a client_credentials token
var idForClientCredentialsOnly = "client=ui&client_only=true";
String finalRequestBody;
var joiner = new StringJoiner("");
if (idForClientCredentialsOnly.equalsIgnoreCase(requestBody)) {
joiner.add("grant_type=").add("client_credentials");
}
else {
joiner.add(requestBody);
if (!containsIgnoreCase(requestBody, "grant_type")) {
joiner.add("&grant_type=").add("password");
}
}
if (!containsIgnoreCase(requestBody, "scope")) {
joiner.add("&scope=").add("uiclient");//I use Keycloak so I specify the scope to get some extra information
}
finalRequestBody = joiner.toString();
return Mono.just(isBlank(finalRequestBody) ? requestBody : finalRequestBody);
};
}
}