I need to fetch the auth token and set it in the header

Question

I'm new to Spring boot and reactive programming.

I'm using spring webflux webclient for an external api service. I need to fetch the auth token and set it in the header

WebClient.builder()
            .baseUrl(baseUrl)
            .filter((request, next) -> {
                return next.exchange(request)
                        .flatMap((Function<ClientResponse, Mono<ClientResponse>>) clientResponse -> {
                            if (clientResponse.statusCode().value() == 401) {
                                return authenticate().map(token -> {
                                    Token accessToken = authenticate().block();
                                    ClientRequest retryRequest = ClientRequest.from(request).header("Authorisation", "Bearer " + accessToken.getAccessToken()).build();
                                    return next.exchange(retryRequest);
                                }).
                            } else {
                                return Mono.just(clientResponse);
                            }
                        });
            })
            .defaultHeader("Authorization", "Bearer " + authToken.getAccessToken())
            .build();


private Mono<Token> authenticate() {
    MultiValueMap<String, String> params = new LinkedMultiValueMap();
    params.add("client_id", clientId);
    params.add("client_secret", clientSecret);
    params.add("grant_type", "password");
    params.add("username", username);
    params.add("password", password);

    WebClient client = WebClient.create(baseUrl);
    return client
            .post()
            .uri(tokenUri)
            .accept(MediaType.APPLICATION_JSON)
            .contentType(MediaType.APPLICATION_FORM_URLENCODED)
            .syncBody(params)
            .retrieve()
            .bodyToMono(Token.class);
}

private static class Token {
    @JsonProperty("access_token")
    private String accessToken;

    public String getAccessToken() { return accessToken; }
}

During the application startup, I'll fetch the access token and set it in the webclient builder. I've created a filter to handle authentication failures after token expiry. But the above code throws error because I've used block() which is not supposed to be used in a reactor thread. How else can I handle it? I'm using oauth2 resource owner password grant flow. Is there is any other way to handle the flow?

Kevin Hussey · Accepted Answer · 2018-10-03T08:13:24.017

5

Hi I had the same issue (Adding a retry all requests of WebClient) which looks like you have reused. but here flatmap is your friend, if you have a Mono<Mono<T>> you can flatten it with flatMap

builder.baseUrl("http://localhost:8080")
             //sets the header before the exchange
            .filter(((request, next) -> tokenProvider.getAccessToken()
                                .map(setBearerTokenInHeader(request))
                                .flatMap(next::exchange)))
            //do the exchange
            .filter((request, next) -> next.exchange(request)
                    .flatMap(clientResponse -> {
                        if (clientResponse.statusCode().value() == 401) {
                          //If unauthenicated try again 
                            return authenticate()
                                    .flatMap(Token::getAccessToken)
                                    .map(setBearerTokenInHeader(request))
                                    .flatMap(next::exchange);
                        } else {
                            return Mono.just(clientResponse);
                        }
                    }))
            .build();

private Function<String, ClientRequest> setBearerTokenInHeader(ClientRequest request) {
        return token -> ClientRequest.from(request).header("Bearer ", token).build();
    }

edited Oct 03 '18 at 08:13

answered Oct 03 '18 at 04:47

Kevin Hussey

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Thank you for your response. Yes, I followed your answer :) Here you've used token.getAccessToken() which will be a mono in my case. How do I set it in header? – kirupakaranh Oct 03 '18 at 07:20
Can you share the signature for authenicate() and Token? You should be able to flatten them if Mono> – Kevin Hussey Oct 03 '18 at 07:21
Thank you! It worked. :) I followed exactly what you've done here. But doesn't it send auth token request for every request since we're not setting it as default header? – kirupakaranh Oct 03 '18 at 08:02
Can you share the signatures of 'authToken.getAccessToken()', you'll probably need to set this before the next.exchange() ... I've updated the example – Kevin Hussey Oct 03 '18 at 08:09
That's just a simple getter.. I've added the code in question – kirupakaranh Oct 03 '18 at 08:17

score 0 · Answer 2 · answered Feb 06 '21 at 04:19

I know this is an old thread, but I could not find any other working examples for the initial question

Basically, I was not able to write a working code from the above examples... With the main task: Use WebClient instance to get protected resource by providing Bearer token. The Bearer token can be requested by a separate request.

The Mono authenticate() should work fine to get a new token.

        WebClient client2 =  WebClient.builder()
                                    .baseUrl(SERVER_URL)
                                    .filter((request, next) -> {
                                        return next.exchange(request)
                                                .flatMap( clientResponse -> {
                                                    if (clientResponse.statusCode().value() == 401) {
                                                        return authenticate().map(token -> {
                                    Token accessToken = authenticate().block();
                                    ClientRequest retryRequest = ClientRequest.from(request).header("Authorisation", "Bearer " + accessToken.getAccessToken()).build();
                                    return next.exchange(retryRequest);
                                });
                                                    } else {
                                                        return Mono.just(clientResponse);
                                                    }
                                                });
                                    })
                                    .defaultHeader("Authorization", "Bearer " + token.getAccessToken())
                                    .build();

For the above example was not able to replace the ".block()" with flatMap()

And the second example

        WebClient client3 =  WebClient.builder().baseUrl("http://localhost:8080")
                                 //sets the header before the exchange
                                .filter(((request, next) -> tokenProvider.getAccessToken()
                                                    .map(setBearerTokenInHeader(request))
                                                    .flatMap(next::exchange)))
                
                                //do the exchange
                                .filter((request, next) -> next.exchange(request)
                                        .flatMap(clientResponse -> {
                                            if (clientResponse.statusCode().value() == 401) {
                                              //If unauthenicated try again 
                                                return authenticate()
                                                        .flatMap(Token::getAccessToken)
                                                        .map(setBearerTokenInHeader(request))
                                                        .flatMap(next::exchange);
                                            } else {
                                                return Mono.just(clientResponse);
                                            }
                                        }))
                                .build();

Not sure what is the "tokenProvider.getAccessToken()" and ".flatMap(Token::getAccessToken)" won't accept Due to

    class Token {
        String token = "";
        
        public String getAccessToken() { return token; }
    }

Sorry I'm new to this. If you had a working example please share in this thread

I need to fetch the auth token and set it in the header

2 Answers2