I'm using ADALiOS v3.0.0-pre.2 to connect to Azure AD B2C and authorize a given user. I successfully obtain an accessToken for the user, who gets prompted with UI to login in the process. I use the acquireTokenWithScopes method on ADAuthenticationContext instance to do so.
Somewhere down the line, I want to make sure that the accessToken I obtained earlier is still valid and hasn't been revoked. So, I use acquireTokenSilentWithScopes to check. However, I get an immediate error back saying:
Error raised: 10. Additional Information: Domain: ADAuthenticationErrorDomain Details: The user credentials are need to obtain access token. Please call the non-silent acquireTokenWithResource methods.
What's the right usage of this API such that the token gets silently refreshed or throws an error only when it has been revoked on the server side?
I've managed to beat acquireTokenSilentWithScopes into submission by making the following changes to ADALiOS v3.0.0-pre.2.
ADUserIdentifier has the following class method:
+(BOOL) identifier:(ADUserIdentifier*)identifier matchesInfo:(ADProfileInfo*)info
In it, there are the following lines of code:
NSString* matchString = [identifier userIdMatchString:info];
if (!matchString || [matchString isEqualToString:identifier.userId])
{
return YES;
}
For one reason or another, matchString can sometimes come back as NSNull and calling isEqualToString: method on it will throw. I changed it thusly:
id matchString = [identifier userIdMatchString:info];
if (!matchString || ![matchString isKindOfClass:[NSString class]] || [matchString isEqualToString:identifier.userId])
{
return YES;
}
This seems like a legit bug in the framework that's worth fixing.
When a token is received from AD, ADALiOS tries to store that value in the cache. At some point, it calls ADTokenCacheStoreItem's userCacheKey property, which is defined as follows:
-(NSString*)userCacheKey
{
switch (_identifierType)
{
case OptionalDisplayableId:
case RequiredDisplayableId:
return _profileInfo.username;
case UniqueId:
return _profileInfo.subject;
}
}
In my case, I use RequiredDisplayableId to identify users. In the switch statement above, that translates to _profileInfo.username, which, in turn, returns the preferred_username value from the user profile dictionary. For me that value is not set. So, userCacheKey returns NSNull and the caching mechanism fails.
The values that are set in the user profile dictionary are name and tid. This could be a server misconfiguration, but I worked around the issue by changing the return value of this method to _profileInfo.friendlyName (which maps to name in the user profile dictionary).
The ADKeychainTokenCacheStore, which I use as the concrete ADTokenCacheStoring cache of choice, exposes a sharedGroup property that allows multiple applications to share common keychain secrets. By default, sharedGroup is set to com.microsoft.adalcache. However, since the class is currently private, there is no way to override this value. Also, having that value set requires the iOS app to declare the shared group name in its entitlements. Without these entitlements properly configured, setting values into the keychain fails. So, to work around this issue, I manually set the default sharedGroup value to nil in the ADKeychainTokenCacheStore class itself. I suspect eventually this class will be exposed by the framework as public, but currently that's not the case so I had to hack into it.
When I request an auth token from the AD server via the ADALiOS framework, I do so using a policy and a set of scopes. The framework code uses this policy/scope pair to create a lookup key and see if any tokens for that key have already been cached. If none are found, the code contacts the server as expected. Once the server returns an auth token, the framework attempts to cache the value. It constructs a brand new policy/scope key object. However, this time, it uses the policy and scope values that are returned by the server, not the ones I passed in. And, for some reason, the server returns those values to nil. As a result, the new policy/scope key that gets constructed for storage is valid but different from the one I used to look up the cached token initially. So, while the caching operation succeeds, next time I try to look up the auth token using my valid policy/scope pair, the lookup fails.
This may, once again, be a server misconfiguration issue.
Regardless, to fix the problem, I now reset the policy and scope values in the response from the server to the original values I used to generate the server request in the first place. This happens in the following method in ADAuthenticationContext(TokenCaching):
- (void)updateCacheToResult:(ADAuthenticationResult*)result
cacheInstance:(id<ADTokenCacheStoring>)tokenCacheStoreInstance
cacheItem:(ADTokenCacheStoreItem*)cacheItem
withRefreshToken:(NSString*)refreshToken
After all these changes, getting the AD auth token and refreshing it silently seems to work as expected. I'm a little worried about how much I needed to hack into the codebase to make it work. It would be helpful if some MS folks could direct me as to whether these changes were warranted or whether there is a more straight-forward solution.
UPDATE: It turns out that you don't need to hack into ADKeychainTokenCacheStore directly (change #3 above). The ADAutheticationSettings class exposes a method for you to do so thusly:
[[ADAuthenticationSettings sharedInstance] setSharedCacheKeychainGroup:nil];