fix(auth): oidc group can be a string

src/main/java/org/akhq/modules/OidcUserDetailsMapper.java

@@ -106,7 +106,7 @@ protected String getUsername(Oidc.Provider provider, OpenIdClaims openIdClaims)
 
     /**
      * Tries to read groups from the configured groups field.
-     * If the configured field cannot be found or isn't some kind of collection, it will return an empty set.
+     * If the configured field cannot be found or isn't some kind of collection or string, it will return an empty set.
      *
      * @param provider     The OpenID provider configuration
      * @param openIdClaims The OpenID claims
@@ -116,11 +116,15 @@ protected List<String> getOidcGroups(Oidc.Provider provider, OpenIdClaims openId
         List<String> groups = new ArrayList<>();
         if (openIdClaims.contains(provider.getGroupsField())) {
             Object groupsField = openIdClaims.get(provider.getGroupsField());
+            // When the user belongs to only one group, groupsField can either be an array (with one item)
+            // or a string, depending on the IdP implementation.
             if (groupsField instanceof Collection) {
                 groups = ((Collection<Object>) groupsField)
                         .stream()
                         .map(Objects::toString)
                         .collect(Collectors.toList());
+            } else if (groupsField instanceof String) {
+                groups.add((String) groupsField);
             }
         }
         return groups;

src/test/java/org/akhq/modules/OidcAuthenticationProviderTest.java

@@ -95,6 +95,38 @@ void successSingleOidcGroup() {
         assertEquals("test.*", ((List<?>) response.getAuthentication().get().getAttributes().get("topicsFilterRegexp")).get(0));
     }
 
+    @Test
+    void successSingleStringOidcGroup() {
+        JWTClaimsSet claimsSet = new JWTClaimsSet.Builder()
+                .claim(OpenIdClaims.CLAIMS_PREFERRED_USERNAME, "user")
+                .claim("roles", "oidc-limited-group")
+                .build();
+        JWT jwt = new PlainJWT(claimsSet);
+
+        Mockito.when(tokenEndpointClient.sendRequest(ArgumentMatchers.any()))
+                .thenReturn(Publishers.just(new OpenIdTokenResponse()));
+        Mockito.when(openIdTokenResponseValidator.validate(ArgumentMatchers.any(), ArgumentMatchers.any(), ArgumentMatchers.any(), ArgumentMatchers.any()))
+                .thenReturn(Optional.of(jwt));
+
+        AuthenticationResponse response = Flowable
+                .fromPublisher(oidcProvider.authenticate(null, new UsernamePasswordCredentials(
+                        "user",
+                        "pass"
+                ))).blockingFirst();
+
+        assertTrue(response.isAuthenticated());
+        assertTrue(response.getAuthentication().isPresent());
+        assertEquals("user", response.getAuthentication().get().getName());
+
+        Collection<String> roles = response.getAuthentication().get().getRoles();
+
+        assertThat(roles, hasSize(4));
+        assertThat(roles, hasItem("topic/read"));
+        assertThat(roles, hasItem("registry/version/delete"));
+
+        assertEquals("test.*", ((List<?>) response.getAuthentication().get().getAttributes().get("topicsFilterRegexp")).get(0));
+    }
+
     @SuppressWarnings("unchecked")
     @Test
     void successWithMultipleOidcGroups() {