I am building a asp.net webapi which is protected by Azure AD Oauth bearer token authentication. I am using Azure AD Bearer token validation OWIN middle-ware to validate the token and extract the claims.
I have a requirement to differentiate when a request is coming from a service context and when the request coming from user context. I am aware that App Tokens (Issued by AD for a APP context) will not have any UPN claims using which i can easily identify but i was wondering is their any standard way to do this?
Quoting from an internal forum:
The appidacr claim indicates the type of client authentication performed. For a confidential client, the value is 1 when a shared secret (a password) is used as a client secret and 2 when a certificate is used as a client secret. The value 0 indicates a public client, which does not provide a client secret and therefore does not authenticate to the STS. Since confidential clients can acquire both user delegated and app only access tokens, the appidacr claim alone does not help to distinguish a user token from an app-only token.
If you want to distinguish between app-only access tokens, user-delegated access tokens, and id tokens issued by Azure AD (all of which are JWTs signed by the same key), follow this guidance:
First of all, validate the ver claim's value is 1.0.
Next, check to see if the JWT is an access token or an id token. The most reliable way to distinguish between the two is the presence of the appid and appidacr claims. These claims will be present in access tokens, but not id tokens.
If the JWT is an id token, then it represents a user. The subject of an id token issued by Azure AD is always a user. Never accept an id token as proof of authentication, always require an access token.
If the JWT is an access token, the presence of an scp (scope) claim informs you that the token is a user delegated access token. The value of the scp claim tells you what authorization the client has been granted by the user.
If the access token does not have an scp claim, it is an app-only access token. In this case, it may have a roles claim.
Don't rely on UPN and email claims to determine the type of token, they're not as reliable.
Per the Microsoft Docs
Your application may receive tokens on behalf of a user (the usual flow) or directly from an application (through the client credentials flow). These app-only tokens indicate that this call is coming from an application and does not have a user backing it. These tokens are handled largely the same, with some differences:
App-only tokens will not have a scp claim, and may instead have a roles claim. This is where application permission (as opposed to delegated permissions) will be recorded. For more information about delegated and application permissions, see permission and consent in v1.0 and v2.0.
Many human-specific claims will be missing, such as name or upn.
The sub and oid claims will be the same.
Personally in my code, to determine if a token is an App token, I use a combination of checking that the claims: "oid" and "sub" both exist and are the same, as well as checking that the token does not contain a name claim.
In practice I have found that tokens issued using different flows can contain different claims, which is why I have found using a combination of a couple of these properties can lead to better being able to differentiate between a user and application token.
There is now a supported way of telling whether or not the token is for an App or not.
Azure Ad supports the configuring of access tokens, for your protected resource to have some optional claims. The claim needed to answer "Is token for App?" is "idtyp"
See Configuring optional claims for how to set it up
Related
I am new to the Azure ecosystem and I am a bit lost.
I use Azure AD B2C to secure multiple Spring Boot applications but I have a strange behavior, it seems like a token is tied to a specific application, which is not really convenient, because that means we have to manage multiple tokens, one per application. On each application I have this configuration:
azure:
activedirectory:
b2c:
base-uri: https://<tenant>.b2clogin.com/
tenant-id: <tenant-id>
client-id: <client-id>
user-flows:
sign-up-or-sign-in: B2C_1_signin_signup
Example, I have a user UserA which wants to consume ApplicationA, ApplicationC and ApplicationD. UserA relies on ApplicationB(front end app) to ask a token using the grant_type=password.
When I use the granted access token I can only consume one application. If I try to use the same token in another application I have a HTTP 401 with this message in application logs:
The aud claim is not valid
The issue is, when we ask a token we can only specify one scope, the scope value should contain the application that should consume the token.
My question is: how can we use one token for multiple resource servers? How can I configure Azure AD B2C to add all applications in the aud claim so that the token is recognized by the resource server?
Thank you
The requested scope determines which API the access token can be used at. The access token aud claim will be set to the client id of the respective scope.
You can use the refresh token you acquired in the first authentication to request an access token for a different scope.
The subsequent scope you request as part of a refresh token call, must be granted as a permission under the first application (app registration) that you authenticated to. It doesn’t matter which scope was requested in the initial authentication at this point.
In the Microsoft Azure AD Documentation the JWT Token validation process is described as validating the token signature and then validating its claims.
So, the validation happens entirely on the client side, without asking the Azure AD server whether the token is still valid.
Is there any option for "extended" validation of the token, i.e. by querying for the Azure server, so that the application granting the access to the resource could be sure that the person is still authorized and has an access to that resource.
No, access is granted for the lifetime of the token.
Tokens have an expiration date that you can read from the exp claim. You can control the expiration of a token which then requires the user to reauthenticate after expiration.
If you want to do extended validation, you will need to implement that logic.
ID Tokens
Access Tokens
Configurable token lifetimes in Azure Active Directory
Trying to set up Azure AD OAuth client credentials grant flow for my web api. I'm following the document in https://learn.microsoft.com/en-us/azure/active-directory/develop/v1-oauth2-client-creds-grant-flow. I have to expose my API to a 3rd party. I've created the APP in Azure AD (this is for the client that is requesting my API), generated the secrets and was able to get a response from oauth2/token endpoint. My questions are below:
What is the best way to validate the token? Is it by passing the JWT
(bearer token) as a HTTP header to my API, and then using the SDK to
validate the token
(System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler)? I'm using
C#.
What is the significance of Azure AD -> App Registrations -> "My
API App" -> under Manage, Expose an API? It has an option to
"Authorize client applications". How could I use this feature to
conditionally block and approve the client applications?
I will have to share the secret, client id and the App Id Uri with the 3rd party for them to generate the token and I will validate the token when I receive it.
You're on the right track.
This answer, Azure AD OAuth client credentials grant flow with Web API AuthorizeAttribute Roles, will walk you through one way to do this, using the roles claim in the token to authorize the call.
You will need to:
define roles
create an App registration for each 3rd party
assign their application to your desired roles
You can then use the AuthorizeAttribute to map which roles can execute which controllers/actions, like so:
[Authorize(Roles = "Reader,Requester,Editor,Approver,Administrator")]
Token validation
Once you complete token obtaining flow, you receive a JWT bearer access token. From token consuming end (your service), you need to perform a JWT validation. This is done by validating JWT signature and Claims. One of the most important claim you validate is the audience (aud) claim which must be the identifier (ex:- your service's URL, an ID) unique to token receiving service. Where you register this ? That's your second question.
Please read through MS's guide on token validation which explains key points - Microsoft identity platform access tokens
Service registration
This is where you register valid token receivable endpoints (ex:- your api app). If you check your token request, you provide resource parameter which must match to registered identifier. This allows Azure to validate the token request and issue an access token the mentioned resource. You find this as aud claim in the token. Hope you got the connection now.
App secret
No, only the token obtaining party require the client credentials. Your API or any token consuming party does not need the secret. They only require a valid access token and token signing certificate details. certificate details are exposed at jwks_uri in openid-configuration endpoint.
I already made the authentication flow with the Microsoft Graph/Azure AD authentication. Once I get the authenticated user's token I store them in his cookies. To validate the user's token I call the Microsft Graph API resource /me. This does not seem a good approach because basically everytime time a client does a request to my API, he is basically doing 2 requests because my API requests Azure AD for validation.
Is this a good flow?
No, it isn't.
Your front-end should acquire an access token for your API, which the API can verify using its digital signature.
The token will contain some info about the user as well as the app that acquired it.
The way in which the front-end acquires the token depends on the type of application.
Front-end single page apps use implicit grant flow for example.
Do note that you have to specifically ask for an access token for your API.
As long as your back-end is then configured with standard JWT Bearer authentication,
all is handled.
This is done by specifying the authority as your Azure AD tenant (or the common endpoint if it's multi-tenant),
and the standard bits for JWT authentication should download the public keys from Azure AD's metadata endpoint, which it can then use to verify validity of any access token it receives.
You do not have to validate tokens for an api that's not yours (issued to your AppId Uri).
For example, Graph validates the tokens that are sent to it (issued for "https://graph.microsoft.com).
If you build and register in Azure AD an Api of your own (say AppIdUri="https://myapi.mydomain.com"), your clients will request and receive access tokens with aud claim set to "https://myapi.mydomain.com".
The clients themselves don't need to validate the access token issued for your Api But your Api, when it receives those access tokens, has to validate them. The validations, among other things will validate the access token was issued to "https://myapi.mydomain.com".
Try out this sample, to get a good understanding around concepts of token validation.
I need clarification with sample or reference link for below items:
How to enable automatic renewal of access token?
How to get active access token and expiry time ?
Is there any possible ways to get Ad username, password and client id again from access token?
How to validate access token ?
It all needs to be implement in c# not in powershell.
How to enable automatic renewal of access token?
Upon successful authentication , Azure AD returns two tokens: a JWT access token and a JWT refresh token .When the access token expires, the client application will receive an error that indicates the user needs to authenticate again. If the application has a valid refresh token, it can be used to acquire a new access token without prompting the user to sign in again. If the refresh token expires, the application will need to interactively authenticate the user once again.
How to get active access token and expiry time ?
For how to authenticate users and get an Azure AD access token for your azure ad app , you could refer to Authentication Scenarios for Azure AD .The Azure Active Directory Authentication Library (ADAL) enables client application developers to easily authenticate users to cloud or on-premises Active Directory (AD), and obtain access tokens for securing API calls. ADAL is available on a variety of platforms. You could find code samples and common scenario in this document .
Is there any possible ways to get Ad username, password and client id again from access token?
You could get decode the access token , find the upn claim which Stores the user name of the user principal ; appid claim identifies the application that is using the token to access a resource. Please refer to document :Azure AD token reference .And of course ,you can't get password information .
How to validate access token ?
JWT tokens are signed, but not encrypted when received. It must validate the signature to prove the token's authenticity and validate a few claims in the token to prove its validity. The claims validated by an app vary depending on scenario requirements, but there are some common claim validations that your app must perform in every scenario.For example, we need to verify the iss and aud claim if you were developing a single tenant app. And you also need to verify the nbf to ensure the token is not expired. For more details , please refer to Validating tokens .
Here is a code sample for how to manually validating a JWT access token in a web API . And if you were using the OWIN components in your project, it is more easy to verify the token by using UseWindowsAzureActiveDirectoryBearerAuthentication extension , code sample here is for your reference .