Unexpected 401 Unauthorized scenarios with OAuth2 Token Refresh in Spring Boot App
I'm prototyping a solution and I've been struggling with this for a few days now and could really use some help... I'm currently working on a Spring Boot application that uses OAuth2 for authentication, specifically Spring Security 5.4. I have implemented a token refresh mechanism using a refresh token, but I am working with an unexpected `401 Unauthorized` behavior after the refresh token is sent to the `/oauth/token` endpoint. Initially, I can authenticate users and retrieve both the access and refresh tokens without any issues. However, after the access token expires, the refresh token request fails with the behavior message: `Invalid refresh token`. I have verified that I am sending the correct refresh token, yet it seems to be invalid. Here’s an example of the code I’m using for the token refresh: ```java public ResponseEntity<?> refreshAccessToken(String refreshToken) { Map<String, String> requestBody = new HashMap<>(); requestBody.put("grant_type", "refresh_token"); requestBody.put("refresh_token", refreshToken); HttpHeaders headers = new HttpHeaders(); headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED); HttpEntity<Map<String, String>> requestEntity = new HttpEntity<>(requestBody, headers); return restTemplate.exchange(tokenEndpointUrl, HttpMethod.POST, requestEntity, String.class); } ``` I also have the following configuration in my `application.yml`: ```yaml spring: security: oauth2: client: registration: my-client: client-id: my-client-id client-secret: my-client-secret authorization-grant-type: authorization_code redirect-uri: http://localhost:8080/login/oauth2/code/my-client scope: read,write provider: my-provider: authorization-uri: https://oauth.example.com/auth token-uri: https://oauth.example.com/token user-info-uri: https://oauth.example.com/userinfo ``` I've tried checking the validity of the refresh token in my database and verified that it is still active. Also, I made sure that the token endpoint URL is correct and that the client secret is being sent properly. I suspect there might be an scenario with token storage or token expiration handling. Has anyone experienced a similar scenario or have any insights on how to debug this scenario further? Am I missing something obvious? Any ideas how to fix this?