That question is hardly related to AppLinks assetlinks.json appears not to be used for validation
I am implementing Oauth2 apps on Android. I would like to do SSO (single sign-on) and I have a concern about AppLink to secure the Autorization Code.
The native app, through the browser, initiate an Authorization Request and then receive an Authorization Response containing the Authorization Code. According to RFC6749#section-4.1.2, the code is passed inside the URL:
Location: https://client.example.com/cb?code=SplxlOBeZQQYbYS6WxSbIA&state=xyz
Authorization Code is a sensitive piece of information because it allows a client to fetch an Access Token and Refresh Token and then access to a protected ressource.
To protect that code, the native app must implement https scheme redirects (RFC8252#section-7.2 & section-8.1). On Android, that must be done using the assetlinks.json file
But according to the related question linked at the top, app links on Android seems not to be 100% secure, because the OS may not verify the https scheme.
In that context, how are we supposed to implement Oauth2 authorization code hook ?
EDIT
According to #benjamin anwser, AppLink is not for security. But, the related threat use-case is the following : a malicious app is installed and uses the "SSO Cookie" to get the Auth Code and exchange it for AT+RT. It seems to me that nothing in the process can prevent that case: if applink is not for security, how does the Authorization Server can be aware that this app is a malicious app ?
Note: By SSO-Cookie, I mean the use of CustomTab to do SSO on Android.
It's not the AppLinks functionality that guarantees security. When you configure the /.well-known/assetlinks.json file it allows a transparent redirect to the application without any user interaction. This means that the modal dialog that usually appears to chose which application the user would like use to handle the link won't pop.
As you stated, this mechanism can be bypassed if the user chooses to handle your link with another app or your app is not yet install. The user needs to go to the phone setting in order to achieve this :
Settings > Apps > choose the application which can handle the Authorization Code link > Open by default > Open supported links in this app > choose Always allowThis way a third party application can catch the information contained in your link, in your case the Authorization Code.
That been said, it's actually the Proof Key for Code Exchange (PKCE) that guarantees security of Authorization Code. Your server must implement this feature in order to mitigate unwanted Authorization Code replays.
A little reminder on the OAuth authorization steps using PKCE :
The client (application) calls the /authorization endpoint with a hashed random string and the method which was used to hash it. The client keeps the random string (not hashed) because it will used in the step 3.
The authorization server checks if user entered a right login/password. If all it's good, it stores the hashed random string and it's hash method which were sent in the request. The server then redirect the user agent to the application with a redirection containing the Authorization Code.
In order to retrieve it's Access Token, the client (application) calls the /token endpoint with random string generated in step 1.
The server receives the /token request, extracts the random string and hashes it with the method stored in step 2. Then the server must checks that this hashed string matches the one stored in step 2. If the strings are the same, the server responds with an Access Token and a Refresh Token, otherwise with an error.
This is how the PKCE ensures that the client that made the /authorization request it's the same client that will make the /token request. So even if a third party app captures your Authorization Code it can't use it to retrieve Acess Tokens.
For more informations see : PKCE (rfc 7636) and OAuth 2.0 for Native Apps (rfc 8252)
Related
Currently, we have the following landscape: a back-end (Play + Scala) server that provides a RESTful API. In addition we have a front-end Web client and an Android native app client. Now we want to add the WSO2 Identity server (v 5.1) to maintain user logins everywhere.
The problem that I am facing is with the native android app integration. I have a successful Google Sign In and as a result I have the Open ID token. According to https://developers.google.com/identity/sign-in/android/backend-auth I should send the token to my back-end server (WSO2IS) where the token should be verified against Google authorities and if the token is legit, it should sign in my user in WSO2IS. Note that if such user doesn't exist in our system, it should first be created and then signed in. Unfortunately I don't find a way to send the token to WSO2 Identity Server.
What I have done so far:
1) configured Identity Provider (IDP Google Federated Authenticators)
2) configured Service Provider where Local & Outbound Authentication Configuration points to previously defined Federated Authenticator Google
3) configured some claims in both IDP and SP
Then I start playing with the endpoints:
/oauth2/token
/oauth2/authorize
But using this is not what I want, because these endpoints will generate me a new token instead of getting the one I have.
Then I found out about Open ID prompt=none (http://openid.net/specs/openid-connect-core-1_0.html#AuthRequest), and I also tried to invoke authorize and pass the open ID connect as Authorization: Bearer <token> header when I call
oauth2/authorize?prompt=none&scope=openid&client_id=fzOPC3fCftkgC3xcLn7ZqjXiY_Ya&response_type=code&redirect_uri=https%3A%2F%2Flocalhost%3A9443%2Fcommonauth
Also tried none+login.
Is it possible to do this with WSO2IS? To register/login a user by passing a Google Open ID token?
If it turns out what I am trying to do is not possible, I come up with the following workarounds:
1) Create a custom service that will validate the token and if legit will register a new user. This is just an idea, I don't know if it is possible and also if I need to write the code myself why should I use the WSO2 Identity Server?
2) In the Android App I should drop the native Google sign in support and use a WebView where we will use the pretty clear and standard Web App flow. I cannot evaluate what I will lose by using web view instead of the API, but it seems wrong. It is natural that on Android phone you should sign in seamlessly with your Google account.
If I need to use one of the workarounds, please advise me which one is the better approach? Or propose a new one.
EDIT 1: Workaround 2 discarded based on
Browser popups is the preferred way for web apps to redirect the user to the IdP. Mobile apps on platforms such as Android or iOS should launch the system browser for that purpose. Embedded web views are not be trusted, as there’s nothing to prevent the app from snooping on the user password. User authentication must always occur in a trusted context separate from the app’s context (e.g. the browser).
This is taken from http://connect2id.com/learn/openid-connect#auth-request
If it is not possible to use a WebView (for security reasons) and in Android you can only open the browser, but you cannot command it with startActivityForResult. This means that even if the user sign in, the browser won't close automatically and it will hand out there until the user close it. In addition the browser won't tell your app that the user is logged and the app should find out by itself (honestly I don't know how: you cannot do server push or something similar, because you can sign in with the same Google account on multiple devices; and the second obvious option is server polling but the app doesn't know for which user to ask).
EDIT 2: A new view over things
When configuring Google for a Web Client login, there is a field for authorized URI (the callback that Google invokes to send the token back). For WSO2IS, this is https://localhost:9443/commonauth. So, this should be the URL that we need to send back the token in the Android app. I start testing with Postman, I am sending the following request:
POST /commonauth?code=eyJhbGciOiJSUzI1NiIsImtpZCI6IjhhNDJhODMzN2IxMmI5MzI5NGIyNGU5NDY5ZTViZWIwZGFhMWJlNGUifQ.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.VMspUYeaAVHavEyoK3Hsss0pyZMHu-4QozucTAU-CLXnjAoaFbPBirslX7VpS4wvwHPge0AE5gHpIzAl1el_ufkhiu2NJn_LKo48Ve3HNj9igjnwD2nW_PGOqlYPoWV5UtFlKyUxi72qvLOCkYwsPuKVzA9irD-vGm3U2U3wBu_OQrJzbhdU9lp3aG4F0tQgQi-NPtEZY7Xgu-Om3qmarByhJYjxBPHEWzuyuQ2F9xY65t0mnd7gVAr2F5_aBHemjVx8V9lQc4eyRFjE3g_9ZgYn9xX9w8TwCXO9VpkdVRdFWQ07RFjFz915FO5KX9x4UNAu6H1Jop9ug5oiVCrmFw HTTP/1.1
On server side, this result in an error: Context does not exist. Probably due to invalidated cache. In server logs I found:
DEBUG - Session data key is null in the request {org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultRequestCoordinator}
ERROR - Context does not exist. Probably due to invalidated cache {org.wso2.carbon.identity.application.authentication.framework.handler.request.impl.DefaultRequestCoordinator}
I've looked at the code for DefaultRequestCoordinator, it seems I need 2 more parameters: type and sessionDataKey. I think the type should be set to openid, but how can I get a valid sessionDataKey?
So, Here is what I understand about how Google Oauth2 works.
Every application or a website (client) needs to register its project and get a client_id and a client secret.
The client_id and a redirect uri are used by the client to make an authorization request to the auth url on behalf of the user who is logged in.
When this happens, there is a pop-up and the user(resource owner) is prompted to allow or deny access to the user's protected resource for the client.
If the user accepts then the user is redirected to the redirect uri from where the client or the application can get the authorization code.
This authorization code is further exchanged for an access token from the OAUTH URL. This access token is later used in the Api calls the client make.
The problem is with the step 3. I am not running a web app or a website. Rather an application that can make curl function calls. Step 4 and step 5 are doable but, How do I bypass the step 3 as I don't have browser capabilities? Is it even possible?
Also can someone please tell how an android app does it? Because even the android app shouldn't have an inbuilt browser. Thanks in advance
We have the OAuth2 for Devices flow to take care of the problem you are trying to solve See this
The user can authorize the app from a different device that has a web broswer.
Every application or a website (client) needs to register its project and get a client_id and a client secret.
Correction / clarification: Any application that wishes to access private Google data must first be registered on Google Developer console. If the data to be accessed is public then a API key can be used. If the data is private then either Oauth2 credentials must be created or service account credentials.
Oauth2 credentials allow a user to grant an application access to a portion of their data (Denoted by scope) the application is identified by the client id and client secret.
Service accounts would allow for preauthorized access to private data normally owned by the developer working on the application. They do not popup the request for user authentication. Please see my article on this Google Developer console service account I don't want to go into service accounts here as you appear to be concerned with Oauth2.
2 . The client_id and a redirect uri are used by the client to make an authorization request to the auth url on behalf of the user who is logged in.
Correction / clarification: The first step in the Oauth2 dance is to request access from the user. This is done via a web page.
https://accounts.google.com/o/oauth2/auth?client_id={clientid}.apps.googleusercontent.com&redirect_uri=urn:ietf:wg:oauth:2.0:oob&scope=https://www.googleapis.com/auth/analytics.readonly&response_type=code
Redirect uri is used to tell the authentication server where to return the authorization code to. In the event this is a web page application it would be the full location to a webpage capable of handling the next steps in the process. As you can see I have not put a web page in. This is in sense localhost. It tells the authentication server to just return the code to where ever it was I just sent my request from. It is used in windows applications and probably android although I am not an android programmer so I am not sure its just an educated guess.
4.If the user accepts then the user is redirected to the redirect uri from where the client or the application can get the authorization code.
Correction / clarification: Its probably your code that's redirecting you. I don't think its the server redirecting you but I may be wrong. The authentication server can send the code were ever you want it would be up to the developer to redirect the user someplace after the exchange.
5.This authorization code is further exchanged for an access token from the OAUTH URL. This access token is later used in the Api calls the client make.
Correction / clarification: access token is only good for an hour and you might also get a refresh token back which can be used to get a new access token.
Addressing your problems
The problem is with the step 3. I am not running a web app or a website. Rather an application that can make curl function calls. Step 4 and step 5 are doable but, How do I bypass the step 3 as I don't have browser capabilities? Is it even possible?
This is going to depend upon which api you are going for and whos data this is. If this is data owned by your users then request access from them save the refresh token and then when you need to access it again in your curl script you can just get a new access token and you have access. Its only the initial authorization you need to bother your users with.
Second option if this is your data that you personally have access to you may be able to user a service account. Service accounts are like dummy users you can preauthorize their access. I could create a service account add it as a user on a folder in my google drive and it would then be able to read and write to my google drive with out that popup window.
Also can someone please tell how an android app does it? Because even the android app shouldn't have an inbuilt browser. Thanks in advance
I am not an android developer I think part of it is magic in the Android SDK the credentials you get for android apps are even different. Cant really help with this one.
I am writing a Google App Engine application along with a CLI client, an Android client and a Javascript client. The purpose of this application is to allow one to control an Android phone on which the Android client is installed, by using either the CLI or the Javascript client.
Authentication plays a crucial role as a bug might allow a malicious user to control others' phones.
The Android client is written and works. It authenticates the user using this method. Basically, this give me a so-called SACSID token I can store in a cookie. When this cookie is set App Engine recognizes my user. The server application can then call the UserService to get a User on which to call getUserId(). getUserId() returns me an opaque string that identifies my user. So far so good.
Now I am writing the JS and CLI clients.
Because the CLI client has no reliable way of displaying a CAPTCHA or opening a browser, I suppose that it needs to use the Device API ("Client login" is not an option). This API requires using OAuth 2 for authentication. Also, I want the JS client to access the user's contacts, which also seems to indicates that OAuth 2 would be suitable.
If my user authenticates using OAuth 2, will I be hable to somehow transform this Google OAuth 2 token into the same opaque String that I get when the Android client connects ? If not, can I modifiy my Android Application so that it uses OAuth instead of a Sacsid token ?
To be more specific, I see three things that would solve my problem :
A way of getting an OAuth 2 token from the Account Manager
A way of exchanging the OAuth 2 token for a SACSID token
A way of getting the same opaque UserID both with the SACSID token and the OAuth2, but only if I can have both authentication system on the same application.
Something that seems similar to the third possible solution is to get the user's email address from both OAuth and the SACSID token, and to use that as the user ID. This however looks a bit clumsy to me :
Every time I receive an OAuth 2 request, I would need to call Google APIs to retrieve the user's email address (or build my own system of tokens which seems insecure and introduces many other difficulties).
The email address of a given user can change, making me lose the association between the user and his previous data.
Use End Points instead:
https://developers.google.com/appengine/docs/java/endpoints/
They use oauth2, they are easy to implement and have support for android IOS and Web.
Is there any free single-signon mechanism for Android that gracefully works with non-webapps? Say, something along the lines of...
You launch my app and use it until it makes a request from the app server that requires authentication. It responds to that request with a random token that the server will associate with you for a short time.
The app presents you with a username field, a password field, and a submit button.
You enter your username and password. The app then forwards your username and hashed password, along with the token generated by the app server, to the login service.
The login service determines whether or not your username and password are valid. If they are, it digitally timestamps and signs the token, and returns the signed token to the app.
The app relays the signed token to the server.
The server checks the signature, satisfies itself that it's valid and signed by an authority it trusts, and proceeds as though the user had presented IT with a valid local username and password instead.
I suspect I'm just getting lost in nomenclature, but the impression I've gotten so far is that all the usual SSO providers -- Twitter, Facebook, etc -- only allow users to log in using a normal browser, and that you're either not allowed to do what I described, or they do something to make it effectively impossible with anything besides a normal browser (like dynamically creating the login form via Javascript in an effort to prevent developers from trying to use their own apps as a login facade).
Alternatively, does there exist any workflow like THIS...
You launch my app and use it until the web service requires you to log in. The app server generates a token and returns it to the app.
The app spawns a new browser via intent that sends you to the login provider's web site, passing the token via intent to the browser (and ultimately the provider) as a POSTed formvar.
You log in using the browser window, and the browser window closes -- returning you to my app.
The login provider signs the token, then sends it directly to my app server via HTTP POST so I can note its submission, verify the cert, and treat it as though it were instead a valid username and password submitted directly by the user to the app server himself.
Have you tried or think of using Firebase? https://firebase.google.com/docs/auth/?hl=es-419
It has some useful tools, you can sign-in with multiple social connectors and user/password as well, and they provide a library to integrate the whole UI and server flow, they even take advantage of google smart lock for you.
Take a look at https://github.com/firebase/FirebaseUI-Android I used it in a personal project and saved me a lot of time.
What you described in Alternatively section looks like Authorization Code using Proof Key for Code Exchange (PKCE) OAuth 2.0 grant
https://www.rfc-editor.org/rfc/rfc7636
The flow is the following:
Your app generates a random key (code_verifier) and it's transformed value (code_challenge) and navigates to authorization server with code_challenge as a parameter
Authorization server redirects back to your app with authorization code
Your app sends authorization_code and the code_verifier to the auth server to get the authorization token
Server uses authorization_code and the code_verifier (it already has code_challenge, so it can verify that code_verifier is correct) and then returns to your app with the token.
On the practical side of it you can use something like Auth0 to implement it in your app.
Use Android Account Manager for SSO.
Providing references below just for knowledge. You have to dig into account manager.
Android developer: https://developer.android.com/training/id-auth
Blog with example: https://www.zoftino.com/android-account-manager-&-create-custom-account-type
I'm writing an Android application that I want to be able to send requests to a Google App Engine application. In order to do this, the Android app needs to authenticate the user (should be able to just use their Google Account). I'm not sure I'm doing it right, but this is the only way I've found so far:
Post email, password, etc. to https://www.google.com/accounts/ClientLogin
Obtain an authorization token from the aforementioned address
Use the authorization token in the header of the requests to the AppEngine application
But this isn't working (users.get_current_user() still returns None). Is there a right way to do it?
The approach you describe is almost correct. Instead, you need to:
Submit the credentials to ClientLogin and get back the authorization token.
Submit the authorization token to /_ah/login and get back a cookie (and 302 redirect).
Use the returned cookie on all subsequent requests.
This is the process appcfg uses - see appengine_rpc.py for an example of how to use it (and a module you can use, if you're using Python) - specifically, the _Authorize function.