I'm currently working on a project where an iPad application requires access to an existing web application. The iPad application has been developed internally and is therefore a trusted application. However the data provided by the web application is sensitive so we don't want to store client credentials on the iPad. We also want the ability to revoke iPad access without affecting regular user access.
Given the above, the OAuth2 Resource Owner Password Credentials grant/flow was a good fit for our requirements which we've implemented with DotNetOpenAuth since its an established library.
However, we now require some metadata to be added to the access and refresh tokens for the resource server. The authorization server is adding the metadata via the AuthorizationServerAccessToken.ExtraData property in our implementation of the IAuthorizationServerHost.CreateAccessToken method:
public AccessTokenResult CreateAccessToken(IAccessTokenRequest accessTokenRequestMessage)
{
var accessToken = new AuthorizationServerAccessToken();
// Add some extra data to access token
accessToken.ExtraData.Add("server_parameter1", this.ServerValue1);
accessToken.ExtraData.Add("server_parameter2", this.ServerValue2);
// Set ResourceServerEncryptionKey properties etc
return new AccessTokenResult(accessToken);
}
This does exactly what we want for the access token however the same "ExtraData" is not included in the refresh token which causes an issue when the access token expires and needs to be refreshed because we effectively lose the additional data (since the old access token is discarded).
Can anyone advise if its possible to populate the refresh tokens "ExtraData" in the current version of DotNetOpenAuth in a similar way to the access token?
No, I don't think there is currently a way to embed extra data into the refresh token. Let's talk a bit about why this is.
First off, there is no such thing as a trusted iPad app, whether you develop it or not. The problem is that apps you distribute (even internally) can't keep a secret. Any client_secret, certificate, etc., can be cracked. Therefore apps you distribute can't authenticate themselves to the server. If the server can't authenticate the client, the server can't trust the client.
Now let's look at your scenario a bit more (and if you have more feedback, it may be best to continue the discussion on dotnetopenid#googlegroups.com). The client has data that it wants to eventually end up at the resource server. You're currently trying to pass that data through the authorization server first, then via the access token to the resource server. Why is that? Why not just have the client send the data directly to the resource server along with the access token? If the answer is that the resource server shouldn't trust the client, then what you have by sending it by way of the access token is a false sense of security for the reasons given in the above paragraph. If the client could provide false info to the resource server, it could also provide false data to the authorization server.
One valid use of extra data in the access token is data that the authorization server knows for itself -- not data that came from the client. In which case, it can look up that data each time an access token is minted and doesn't therefore have to be stored in the refresh token.
Related
Currently I have this setup:
At login, and in every subsequent request after login, a mobile application that I have built uses Basic Authentication to authenticate the user with a web service that serves the app with information it requests.
On every request the Authorization header is inspected, the password and username are extracted from the header, the password is hashed using a proprietary DLL (so the web service doesn't actually contain the hashing algorithm) and compared to the hashed password associated with the username that is stored in the database.
I have now been asked to include Azure AD SSO in the login options.
After reading much about the topic, this looks seems to me like the setup:
I'm curious about a few things:
Is this setup correct, more or less?
Does the app send the Identity Token to the web service? If so, how does the webservice validate that token?
Is it correct that the webservice can match the Azure Identity to the DB user using one of the claims in the Security Token?
Where do Access Token fit in this picture?
Thanks for the help!
(Side Note: I know that Basic Authentication is not the preferred way to go in the first scenario. This was a temporary decision till we developed the token handling code, it only works using HTTPS and this is an internal application - you wouldn't be able to activate the app unless you have a code we give you)
I have little experience in azure ad but I think we could talk about your case.
First, whatever id token and access token are both jwt token, so to your web service application, you need to use jwt decode library to decrypt the token and get claims it contains. Here we need to know the difference between id token and access token, and I think you'll know that for your web service application, if it's more likely to play the role of an api application, you need to use access token because this token also contains user information. Then you need to add code in your program to decode the token and check if it's a 'valid' token for the request.(Because you've used azure ad to achieve the login part, you don't need to use your custom login part.)
Next, the signing in feature provided by azure ad requires to use account and password in the tenant which azure ad belongs to, the user accounts may look like xx#xx.onmicrosoft.com, it doesn't required to keep sycn with the accounts in your database, so it's difficult and needless for you to compare the user name obtained from the decoded token with those in your database. Because when your web service received the token(id or access token), that means someone has passed the authentication from azure ad. The token contains user information including role, expired time etc. You need to check if the token has expired and if has the correct scope. (Let's see a common situation, microsoft provides many graph apis to call, when accessing these api, we need to provide access token in request head with matching scope, e.g. https://graph.microsoft.com/v1.0/me
requires a delegated api permission of User.Read)
To sum up here, if your web service just required the users in your database to sign in then can be access, id token and access token are both suitable for you because they both contains user name like 'xx#xx.onmicrosoft.com', what you need to do is decode the token and check if the token has expired and whether this user exists in your database(you may set up a mapping between them).
Imagine you're going through a standard OAuth2 process to retrieve an access_token for some third-party API. This is the usual process.
User is redirected to http://some-service.com/login
User successfully logs in and is redirected to some destination http://some-destination.com. In this step, there's usually a code parameter that comes with the request. So the actual URL looks like http://some-destination.com?code=CODE123
I need to use CODE123 to request an access_token that can be used to authorize my future API calls. To do this, there's an endpoint that usually looks like this (I am using Nylas as an example but should be generic enough):
As you can see, it requires me to POST the code from above (CODE123) along with client_id and client_secret like this: http://some-service.com/oauth/token?code=CODE123&client_secret=SECRET&client_id=ID. As a response, I get an access_token that looks like TOKEN123 and I can use this to make API calls.
QUESTION
Until step 2, everything happens in the client side. But in step 3, I need to have client_id and client_secret. I don't think it's a good idea to store these values in the client side. Does that mean I need to have a backend server that has these two values, and my backend should convert CODE123 to TOKEN123 and hand it to the client side?
As you probably know, the question describes the most common (and usually, the more secure) OAuth "Authorization Code" flow. To be clear, here's an approximation of the steps in this flow:
User indicates that they wish to authorize resources for our application (for example, by clicking on a button)
The application redirects the user to the third-party login page, where the user logs in and selects which resources to grant access to
The third-party service redirects the user back to our application with an authorization code
Our application uses this code, along with its client ID and secret to obtain an access token that enables the application to make requests on behalf of the user only for the resources that the user allowed
Until step 2, everything happens in the client side. But in step 3, I need to have client_id and client_secret. I don't think it's a good idea to store these values in the client side. Does that mean I need to have a backend server that has these two values[?]
You're correct, it's certainly not a good idea to store these values in the client-side application. These values—especially the client secret—must be placed on a server to protect the application's data. The user—and therefor, the client application—should never have access to these values.
The server uses its client ID and secret, along with the authorization code, to request an access token that it uses for API calls. The server may store the token it receives, along with an optional refresh token that it can use in the future to obtain a new access token without needing the user to explicitly authorize access again.
...and my backend should convert CODE123 to TOKEN123 and hand it to the client side?
At the very least, our server should handle the authorization flow to request an access token, and then pass only that token back to the client (over a secure connection).
However, at this point, the client-side application (and the user of that client) is responsible for the security of the access token. Depending on the security requirements of our application, we may want to add a layer to protect this access token from the client as well.
After the server-side application fetches the access token from the third-party service, if we pass the access token back to the client, malware running on the client machine, or an unauthorized person, could potentially obtain the access token from the client, which an attacker could then use to retrieve or manipulate the user's third-party resources through privileges granted to our application. For many OAuth services, an access token is not associated with a client. This means that anyone with a valid token can use the token to interact with the service, and illustrates why our application should only request the minimum scope of access needed when asking for authorization from the user.
To make API calls on behalf of a user more securely, the client-side application could send requests to our server, which, in turn, uses the access token that it obtained to interact with the third-party API. With this setup, the client does not need to know the value of the access token.
To improve performance, we likely want to cache the access token on the server for subsequent API calls for the duration of its lifetime. We may also want to encrypt the tokens if we store them in the application's database—just like we would passwords—so the tokens cannot be easily used in the event of a data breach.
OAuth 2.0 has multiple workflows. I have a few questions regarding the two.
Authorization code flow - User logs in from client app, authorization server returns an authorization code to the app. The app then exchanges the authorization code for access token.
Implicit grant flow - User logs in from client app, authorization server issues an access token to the client app directly.
What is the difference between the two approaches in terms of security? Which one is more secure and why?
I don't see a reason why an extra step (exchange authorization code for token) is added in one work flow when the server can directly issue an Access token.
Different websites say that Authorization code flow is used when client app can keep the credentials secure. Why?
The access_token is what you need to call a protected resource (an API). In the Authorization Code flow there are 2 steps to get it:
User must authenticate and returns a code to the API consumer (called the "Client").
The "client" of the API (usually your web server) exchanges the code obtained in #1 for an access_token, authenticating itself with a client_id and client_secret
It then can call the API with the access_token.
So, there's a double check: the user that owns the resources surfaced through an API and the client using the API (e.g. a web app). Both are validated for access to be granted. Notice the "authorization" nature of OAuth here: user grants access to his resource (through the code returned after authentication) to an app, the app get's an access_token, and calls on the user's behalf.
In the implicit flow, step 2 is omitted. So after user authentication, an access_token is returned directly, that you can use to access the resource. The API doesn't know who is calling that API. Anyone with the access_token can, whereas in the previous example only the web app would (it's internals not normally accessible to anyone).
The implicit flow is usually used in scenarios where storing client id and client secret is not recommended (a device for example, although many do it anyway). That's what the the disclaimer means. People have access to the client code and therefore could get the credentials and pretend to become resource clients. In the implicit flow all data is volatile and there's nothing stored in the app.
I'll add something here which I don't think is made clear in the above answers:
The Authorization-Code-Flow allows for the final access-token to never reach and never be stored on the machine with the browser/app. The temporary authorization-code is given to the machine with the browser/app, which is then sent to a server. The server can then exchange it with a full access token and have access to APIs etc. The user with the browser gets access to the API only through the server with the token.
Implicit flow can only involve two parties, and the final access token is stored on the client with the browser/app. If this browser/app is compromised so is their auth-token which could be dangerous.
tl;dr don't use implicit flow if you don't trust the users machine to hold tokens but you do trust your own servers.
The difference between both is that:
In Implicit flow,the token is returned directly via redirect URL with "#" sign and this used mostly in javascript clients or mobile applications that do not have server side at its own, and the client does not need to provide its secret in some implementations.
In Authorization code flow, code is returned with "?" to be readable by server side then server side is have to provide client secret this time to token url to get token as json object from authorization server. It is used in case you have application server that can handle this and store user token with his/her profile on his own system, and mostly used for common mobile applications.
so it is depends on the nature of your client application, which one more secure "Authorization code" as it is request the secret on client and the token can be sent between authorization server and client application on very secured connection, and the authorization provider can restrict some clients to use only "Authorization code" and disallow Implicit
Which one is more secure and why?
Both of them are secure, it depends in the environment you are using it.
I don't see a reason why an extra step (exchange authorization code
for token) is added in one work flow when the server can directly
issue an Access token.
It is simple. Your client is not secure. Let's see it in details.
Consider you are developing an application against Instagram API, so you register your APP with Instagram and define which API's you need. Instagram will provide you with client_id and client_secrect
On you web site you set up a link which says. "Come and Use My Application". Clicking on this your web application should make two calls to Instagram API.
First send a request to Instagram Authentication Server with below parameters.
1. `response_type` with the value `code`
2. `client_id` you have get from `Instagram`
3. `redirect_uri` this is a url on your server which do the second call
4. `scope` a space delimited list of scopes
5. `state` with a CSRF token.
You don't send client_secret, You could not trust the client (The user and or his browser which try to use you application). The client can see the url or java script and find your client_secrect easily. This is why you need another step.
You receive a code and state. The code here is temporary and is not saved any where.
Then you make a second call to Instagram API (from your server)
1. `grant_type` with the value of `authorization_code`
2. `client_id` with the client identifier
3. `client_secret` with the client secret
4. `redirect_uri` with the same redirect URI the user was redirect back to
5. `code` which we have already received.
As the call is made from our server we can safely use client_secret ( which shows who we are), with code which shows the user have granted out client_id to use the resource.
In response we will have access_token
The implicit grant is similar to the authorization code grant with two distinct differences.
It is intended to be used for user-agent-based clients (e.g. single page web apps) that can’t keep a client secret because all of the application code and storage is easily accessible.
Secondly instead of the authorization server returning an authorization code which is exchanged for an access token, the authorization server returns an access token.
Please find details here
http://oauth2.thephpleague.com/authorization-server/which-grant/
Let me summarize the points that I learned from above answers and add some of my own understandings.
Authorization Code Flow!!!
If you have a web application server that act as OAuth client
If you want to have long lived access
If you want to have offline access to data
when you are accountable for api calls that your app makes
If you do not want to leak your OAuth token
If you don't want you application to run through authorization flow every time it needs access to data. NOTE: The Implicit Grant flow does not entertain refresh token so if authorization server expires access tokens regularly, your application will need to run through the authorization flow whenever it needs access.
Implicit Grant Flow!!!
When you don't have Web Application Server to act as OAuth Client
If you don't need long lived access i.e only temporary access to data is required.
If you trust the browser where your app runs and there is limited concern that the access token will leak to untrusted users.
Implicit grant should not be used anymore, see the IETF current best practices for details. https://datatracker.ietf.org/doc/html/draft-ietf-oauth-security-topics-18#section-2.1.2
As an alternative use a flow with response type code; for clients without possibility to securely store client credentials the authorization code with PKCE flow should be your choice.
From practical perspective (What I understood), The main reason for having Authz code flow is :
Support for refresh tokens (long term access by apps on behalf of User), not supported in implicit: refer:https://www.rfc-editor.org/rfc/rfc6749#section-4.2
Support for consent page which is a place where Resource Owner can control what access to provide (Kind of permissions/authorization page that you see in google). Same is not there in implicit . See section : https://www.rfc-editor.org/rfc/rfc6749#section-4.1 , point (B)
"The authorization server authenticates the resource owner (via the user-agent) and establishes whether the resource owner grants or denies the client's access request"
Apart from that, Using refresh tokens, Apps can get long term access to user data.
There seem to be two key points, not discussed so far, which explain why the detour in the Authorization Code Grant Type adds security.
Short story: The Authorization Code Grant Type keeps sensitive information from the browser history, and the transmission of the token depends only on the HTTPS protection of the authorization server.
Longer version:
In the following, I'll stick with the OAuth 2 terminology defined in the RFC (it's a quick read): resource server, client, authorization server, resource owner.
Imagine you want some third-party app (= client) to access certain data of your Google account (= resource server). Let's just assume Google uses OAuth 2. You are the resource owner for the Google account, but right now you operate the third-party app.
First, the client opens a browser to send you to the secure URL of the Google authorization server. Then you approve the request for access, and the authorization server sends you back to the client's previously-given redirect URL, with the authorization code in the query string. Now for the two key points:
The URL of this redirect ends up in the browser history. So we don't want a long lived, directly usable access token here. The short lived authorization code is less dangerous in the history. Note that the Implicit Grant type does put the token in the history.
The security of this redirect depends on the HTTPS certificate of the client, not on Google's certificate. So we get the client's transmission security as an extra attack vector (For this to be unavoidable, the client needs to be non-JavaScript. Since otherwise we could transmit the authorization code via fragment URL, where the code would not go through the network. This may be the reason why Implicit Grant Type, which does use a fragment URL, used to be recommended for JavaScript clients, even though that's no longer so.)
With the Authorization Code Grant Type, the token is finally obtained by a call from the client to the authorization server, where transmission security only depends on the authorization server, not on the client.
I need to interact with an API that only supports OAuth2.
The problem is, I would like to write a purely server side application which should sit there without a GUI polling an API every day.
The API gives me the ability to get the application token programatically, but it looks like I need to implement the entire GUI flow to get the subsequent access token. This is because I need to log in via the application providers web based login screen.
It looks like I then need to get that access token, and copy this out as my server side credential where I recreate it. If that ever expires or goes bad, I'll need to go back via the GUI flow to get my server side access token.
Is my understanding correct here as this feels very clunky?
Specifically:
Can I avoid implementing the process where we link over to the application providers login form?
Is it right that after doing this, I have to unpick an access token and store this within my server side application. I don't appear to have any control over whether that will expire?
I can see that e.g. Facebook specifically support server side and client side flow. I wonder if I'm coming up against limitations in this particular implementation of OAuth 2?
I don't know how you actually want the app to behave, but one thing is certain - you do have to input the user credentials once.
Once you authenticate and authorize (there are a lot of open questions on SO, about automatic authentication), your app will get not only an access token, but also a Refresh Token. A refresh token is just what you need in your use case. You can store it your the server side - A refresh token does not have an expiration time. It lives till the user explicitly revokes permissions.
For any OAuth service provider there is a token exchange endpoint where you can exchange the refresh token for a (refresh token + access token) pair. So, at the backend (your server) you can at any time hit this endpoint - get a short-lived access token and perform the operation that you need to. This saves you all the effort of following the GUI flow every time.
See this link - https://developers.google.com/accounts/docs/OAuth2WebServer#offline
EDIT - Made some changes after reading your comment. You simply need to know how to use refresh tokens in your app.
I've found that the typical solution to the problem I asked in this question is to use XAuth.
Many providers such as Twitter and the application I am currently working against support XAuth to provide a simplified flow without the user interface based authentication.
What is the difference among BasicAuth,OAuth and XAuth?
Using oAuth 2.0, in "authorization-code" Authorization Grant, I first call to "/authorize", get the code, and then use this code within a call to "/token" to get the access-token.
My question: why this is the flow? I guess it is from a security reason, but I cannot figure it out. Why the implementation is this way, and not getting the access-token immediately after the first call ("/authorize")?
Why do we need this code for?
Could it also be that by having this intermediate step prevents the client from seeing the access token?
From O'Reilly book:
Authorization code This grant type is most appropriate for server-side web applications. After the resource owner has
authorized access to their data, they are redirected back to the web
application with an authorization code as a query parameter in the
URL. This code must be exchanged for an access token by the client
application. This exchange is done server-to-server and requires
both the client_id and client_secret, preventing even the resource
owner from obtaining the access token. This grant type also allows for
long-lived access to an API by using refresh tokens.
Implicit grant for browser-based client-side applications The implicit grant is the most simplistic of all flows, and is optimized
for client-side web applications running in a browser. The resource
owner grants access to the application, and a new access token is
immediately minted and passed back to the application using a #hash
fragment in the URL. The application can immediately extract the
access token from the hash fragment (using JavaScript) and make API
requests. This grant type does not require the intermediary
“authorization code,” but it also doesn’t make available refresh
tokens for long-lived access.
UPDATE - yes indeed:
When Should the Authorization Code Flow Be Used? The Authorization
Code flow should be used when
Long-lived access is required.
The OAuth client is a web application server.
Accountability for API calls is very important and the OAuth token shouldn’t be leaked to the browser, where the user may have access to
it.
More:
Perhaps most importantly—because the access token is never sent
through the browser— there is less risk that the access token will be
leaked to malicious code through browser history, referer headers,
JavaScript, and the like.
The authorization code flow is meant for scenarios where 3 parties are involved.
These parties are:
Client
The user with his web browser. He wants to use your application.
Provider
Has information about the user. If somebody wants to access this data, the user has to agree first.
Your (web) application
Wants to access information about the user from the provider.
Now your app says to the user (redirecting his browser to the /authorize endpoint):
Hey user, here is my client id. Please talk to the provider and grant him to talk to me directly.
So the user talks to the provider (requests the authorization code and returns it to your app by opening your callback URL in his browser):
Hey provider, I want to use this app, so they require to access my data. Give me some code and I give this code to the application.
Now your app has the authorization code which is already known by client AND the provider. By handing this over to the provider your app can now prove, that it was allowed by the client to access his data. The provider now issues your (web) app an access token, so your (web) app won't have to redo these steps each time (at least for a while).
In case of other application types where your app is running directly at the client side (such as iPhone/Android apps or Javascript clients), the intermediate step is redundant.
Data on client side is generally considered unsafe. In the case of implicit calls where token is granted in the initial step itself, anyone with the access_token can request for data, the API doesn't know who is calling that API.
But, in the case of web-server apps where the application wants to identify itself, client_id with client_secret is sent along with authorization_code to get access_token, which in future can be sent independently.
Suppose, if access_token is granted initially itself then as client_id and access_token will still be considered exposed, so the app will have to send client_secret in addition to access_token every time to assure that request is really coming from it.
While in the current scenario, after getting access_token, further requests can be made independently without needing client_secret.
One important point is
Perhaps most importantly—because the access token is never sent through the browser— there is less risk that the access token will be leaked to malicious code through browser history, referer headers, JavaScript, and the like.
I think it is like this;
When we use the authorization code, we have 2 verification parts;
1; to verify ownership of the user, because he logs in
2; we know that the client, is really who he says he is because the client is sending his client_secret.
So if we would return the access token on the moment when the user authenticates instead of the authorization code, we know that it is the user requesting it but we dont know that it will be used for the registered client. So for example your webapp.
When we use the 'implicit grant'; (or return the access token instead of authorization code)
1; We know it is the user who is receiving the access token, but there is no need in getting a authorization code because the 'user-agent' based application is not checkable. It is checkable, if you think about it but it is usable for everyone. The client_secret is publicly viewable in the source code of the 'user-agent' based application so everyone can just 'view source code' and copy the client_secret and use this method to verify ownership of the client.
#ksht's answer is basically correct. For those looking for the simple,brief answer it is this:
Because the client app, (browser or native app), can have the delivered token intercepted. The oauth implicit flow does allow this but only under very specific circumstances. In all other cases either the browser can leak info (hacks in the OS, browser bugs , plugins) or for native apps your custom url scheme that maps the redirect url to the app can be intercepted. So the workaround is send back a code instead of a token (over tls) and use PKCE to ensure that the code can be securely exchanged for a token.