fix(iOS): omit state when additionalParameters.state is null

.changeset/tidy-pianos-shave.md

@@ -0,0 +1,5 @@
+---
+'react-native-app-auth': patch
+---
+
+Fix iOS sending `NSNull` as the OAuth `state` when `additionalParameters.state` is null.

docs/docs/usage/config.md

@@ -44,6 +44,7 @@ See specific example [configurations for your provider](/docs/category/providers
   - **register** - (`{ [key: string]: value }`) headers to be passed during registration request.
 - **additionalHeaders** - (`{ [key: string]: value }`) _IOS_ you can specify additional headers to be passed for all authorize, refresh, and register requests.
 - **useNonce** - (`boolean`) (default: true) optionally allows not sending the nonce parameter, to support non-compliant providers. To specify custom nonce, provide it in `additionalParameters` under the `nonce` key.
+- **state** - to specify a custom state, provide it in `additionalParameters` under the `state` key. A random state is generated when the key is absent. Pass `null` to omit the parameter entirely, to support providers that do not echo it back. Only omit it if you understand the CSRF tradeoff, and note that a provider returning a state you did not send will still fail validation.
 - **usePKCE** - (`boolean`) (default: true) optionally allows not sending the code_challenge parameter and skipping PKCE code verification, to support non-compliant providers.
 - **skipCodeExchange** - (`boolean`) (default: false) just return the authorization response, instead of automatically exchanging the authorization code. This is useful if this exchange needs to be done manually (not client-side)
 - **iosCustomBrowser** - (`string`) (default: undefined) _IOS_ override the used browser for authorization, used to open an external browser. If no value is provided, the `ASWebAuthenticationSession` or `SFSafariViewController` are used by the `AppAuth-iOS` library.

packages/react-native-app-auth/index.d.ts

@@ -59,6 +59,8 @@ interface BuiltInParameters {
   display?: 'page' | 'popup' | 'touch' | 'wap';
   login_prompt?: string;
   prompt?: 'consent' | 'login' | 'none' | 'select_account';
+  /** Custom state. Pass null to omit the parameter, for providers that do not echo it back. */
+  state?: string | null;
 }
 
 export type BaseAuthConfiguration = BaseConfiguration & {

packages/react-native-app-auth/ios/RNAppAuth.m

@@ -344,6 +344,16 @@ - (void)authorizeWithConfiguration: (OIDServiceConfiguration *) configuration
     [mutableDict removeObjectForKey:@"state"];
     [mutableDict removeObjectForKey:@"nonce"];
 
+    // A null from JS bridges to NSNull, which is truthy in ObjC, so a plain
+    // ternary would send NSNull as the state. Absent generates, null omits.
+    id requestedState = additionalParameters[@"state"];
+    NSString *state = nil;
+    if (requestedState == nil) {
+        state = [[self class] generateState];
+    } else if (![requestedState isKindOfClass:[NSNull class]]) {
+        state = requestedState;
+    }
+
     // builds authentication request
     OIDAuthorizationRequest *request =
     [[OIDAuthorizationRequest alloc] initWithConfiguration:configuration
@@ -353,7 +363,7 @@ - (void)authorizeWithConfiguration: (OIDServiceConfiguration *) configuration
                                                      scope:[OIDScopeUtilities scopesWithArray:scopes]
                                                redirectURL:[NSURL URLWithString:redirectUrl]
                                               responseType:OIDResponseTypeCode
-                                                     state: additionalParameters[@"state"] ? additionalParameters[@"state"] : [[self class] generateState]
+                                                     state:state
                                                      nonce:nonce
                                               codeVerifier:codeVerifier
                                              codeChallenge:codeChallenge