Merge pull request #49 from openfga/fix/client-cred-content-type

fix: client_credentials content type

Author: rhamzeh

src/main/java/dev/openfga/sdk/api/auth/OAuth2Client.java

@@ -77,7 +77,8 @@ private CompletableFuture<CredentialsFlowResponse> exchangeToken()
 
             Configuration config = new Configuration().apiUrl(apiTokenIssuer);
 
-            HttpRequest.Builder requestBuilder = ApiClient.requestBuilder("POST", "", body, config);
+            HttpRequest.Builder requestBuilder = ApiClient.requestBuilder("POST", "", body, config)
+                    .header("Content-Type", "application/x-www-form-urlencoded");
 
             HttpRequest request = requestBuilder.build();
 

src/test/java/dev/openfga/sdk/api/auth/OAuth2ClientTest.java

@@ -83,6 +83,7 @@ public void exchangeOAuth2Token(String apiTokenIssuer, String tokenEndpointUrl)
                 .verify()
                 .post(tokenEndpointUrl)
                 .withBody(is(expectedPostBody))
+                .withHeader("Content-Type", "application/x-www-form-urlencoded")
                 .called();
         assertEquals(ACCESS_TOKEN, result);
     }