Problem: I am currently working on making a REST Api available to clients (the client in this case is not the normal end user who orders the articles, but the client's Web Api that communicates with my system). In order to order different products in my system, each customer may have several accounts for each country separately. Authentication is done by authenticating the client's WebApi application to my system (machine to machine). So it looks like this should be done using OAuth2 Client Credentials Flow based on the article https://learn.microsoft.com/en-us/azure/active-directory/develop/authentication-flows-app-scenarios#scenarios- and-supported-authentication-flows, but I have doubts about the issue of client accounts for each country separately.
Question: This should be solved by creating a ClientId and ClientSecret for each client account per country separately or, however, one client account should be created, while the country should be sent by the client in each request to the Api or before adding the country as a scope or claim to access token.
Additionally, I am not sure if Client Credentials Flow is a good choice in this situation, so I would be very grateful for any suggestions.
CLIENTS
Ideally each client company should have a single client credential for getting access tokens. In sone cases, such as when there are different legal subdivisions, this can be extended. By default use a single value, but you need to understand your clients.
A client credentials flow between companies can involve stronger credentials if needed, such as JWT client assertions or Mutual TLS - as in this advanced tutorial.
CLAIMS
In your system you should map domain specific data needed for authorization against each client ID. This might include country specific access to products or whatever makes sense for your scenario.
This data can then be either included in access tokens at the time of issuance, or looked up when an access token is first received, then cached for subsequent requests with the same token. Step 3 of my Authorization Blog Post explains a couple of design patterns here.
API REQUESTS
How the client gets data in API requests is interesting:
Is data for all countries owned by the caller? If so let them select the data they want via a country parameter during API requests.
If the API client shoild never be able to see data for a country, that suggests that in at least some cases you need different clients per country.
SUMMARY
Define clients in terms of what makes sense for those companies. Avoid an explosion of clients in order to manage access rights for the same data owner. Exact solutions depend on your domain specific requirements. OAuth is a framework that is meant to be adapted.
If your entire existing data-model silos 'countries' by a concept of an account, then a set of credentials per account might be the easiest.
But it sounds to me that your data-model doesn't fully capture your actual business well. It sounds to me like you have a concept of a 'customer/client' that has access to one of more 'accounts', each representing a country.
So a more correct way to model this might be to structure your API so that a single API client can access all of the related accounts, and your API should perhaps be structured so that the idea of an accountId is somehow passed (usually in the URL for REST apis). For example, each API endpoint can be prefixed with /account/123.
To me this is more of a data-modelling and API architecture question than anything OAuth2-specific.
Related
It seemed like client_credentials flow was appropriate for a machine-to-machine communication between our system and third parties for importing and exporting data.
But if I have two third parties p and q say and users on our system u and v say, then I need to know which of p and q can acces the data of which of u and v.
For example: user u grants access to p (but not to q) and v to q (but not p).
I can give different client secrets to p and q but when they present thir secret to IdentityServer in order to obtain a token I need to know which of p and q it is and add a claim to the token that my controllers can use to determine which of u ad v's data is visible.
I can implement ICustomTokenRequestValidator to intercept the secret and look it up in the configuration context, but the Id column is not in the model class, so I could abuse the Description column as a foreign key to my table of third parties -- seems hacky.
Is there a standard/recommended way to resolve this situation -- that different machines have different data visible to them (different claims in their token)?
If you use client_credentials flow then there is no user-interaction involved.
Each third party should have it's own client with corresponding client credentials. Do not share the same credentials over boundaries, i.e. between different third parties. By having separate clients for separate parties, you minimize the security risk and minimize the impact when having to revoke or change the credentials.
With that said, in the Client Credentials flow the Authorization Server returns a token if the request is valid - it does not know from the request if the user authorized the request or not because the user is not involved. But it authenticates the client. So, if you want to differentiate between several third parties, give them individual clients. If you can't add a claim to the token.
Scopes and claims are the tools to define what a client requests to do. Some authorization can be done in the Authorization Server. For example, an Authorization Server typically only allows a client to request certain scopes.
Use then claims (the data in the token) for a fine grained authorization in the API. It depends on your use case. If the API is supposed to return a filtered result, i.e. only return data from users that are ok with it, then the API needs to be able to look this information up somewhere, as #gary-archer states. Use an applicable claim from the token that enables the API to identify the client or third party. It can then use this data for the lookup. For example, use the client_id claim but it really depends on the Authorization Server which claims it adds to the token.
If the client already knows beforehand which user's data it is going to access, it could add the user-id when requesting the token and - once again - depending on the capabilities of the Authorization Server - get a token with a user_id in the claim set. Then the API can use the client_id and user_id for a lookup.
How you collect the users' consent is out of scope and happens out of bound. It's part of your business logic.
At the end it is all about designing the token. Here is another article on Centralizing Identity Data
The standard option here is to include custom claims from your business data at the time of token issuance. Rather than machine to machine I would describe your scenario as B2B.
EXAMPLE USE CASE
Consider an API called by business partners who act as suppliers of inventory to your system. In this case a useful access token might look like this, and is what I would aim for:
{
client_id: 1hvf367g
supplier_id: 42
exp: ...
}
API requests for stock items could then authorize based on the supplier_id value in the access token. Eg by running a SQL query on the business data, filtering on the supplier ID. All of this keeps your API code simple.
DATA MAPPING
For this to work you need to design onboarding. Eg a button click to create a supplier in your system might create the OAuth client using Identity Server, then save the client_id to a suppliers table in the business data.
Not all identity systems support issuing custom claims in the above manner. An alternative design is to just include the client_id in the access token, and look up the supplier ID from business data when your API receives an access token. This tends to add complexity to API code though.
SUMMARY
I think your question is really about designing business permissions, and OAuth alone cannot solve it. If I'm right then the Claims Best Practices article may be useful.
Assume my company is offering 2 applications, say Mail and Calendar.
Both applications are using OAuth 2 to secure access.
Now Calendar wants to access data from Mail. If those were applications from two different vendors it would be natural for Calendar to ask the user to authorize it's access to Mail etc.
But since the applications come from the same source I'd like them to be able to share data without the user having to explicitly give permissions.
Or to put it differently: I have ID/Access/Refresh tokens for Calendar. How can I exchange them for an Access Token for Mail without bothering the user?
How can this be done in OAuth 2? I control both the applications and the Identity Provider.
The only solution that comes to my mind is for both Mail and Calendar to be the same Application, but that doesn't seem right (and has other issues, e.g. if you want to restrict someone's access to one of them). I could also implement special access outside of OAuth 2 but that is even worse.
A real world example would be Gmail and Google Calendar. They both present OAuth 2 interface to the outside world, but you don't have to allow them to talk to each other.
PS. References to white papers or cases studies would be appreciated
SEPARATED CLIENTS
By default in OAuth you would register multiple clients which get their own tokens. You would then use Single Sign On when navigating between them the first time:
Client ID: app1
Scope: openid scope1
Redirect URI: https://app1.mycompany.com
Client ID: app2
Scope: openid scope2
Redirect URI: https://app2.mycompany.com
If user consent is involved the user has more choice this way of how they grant access to their personal assets.
COMBINED CLIENT
You could potentially combine these into a single entry like this. Note that there is usually a hosting prerequisite of a single base domain in order for token / cookie storage to work:
Client ID: combinedapp
Scope: openid scope1 scope2
Redirect URIs: [https://app1.mycompany.com https://app2.mycompany.com]
PROS AND CONS
The first option is cleanest most of the time, since you avoid tokens with access to too much data. The second option can make sense for related micro-UIs that are really a single app with the same permissions.
APIs AND SCOPES
To share data across apps, companies build API endpoints. You can then have multiple apps that each use scopes representing multiple business areas. See the Scope Best Practices article as a starting point for designing authorization. Eg user logs into calendar app with scopes openid calendar mail - and therefore can get mail data also.
I'm trying to better understand how to make use of OIDC/OAuth in securing a restful API, but I keep getting lost in terminology. Also when I research this question most of the answers are for Single Page Apps, so for purposes of this question assume the API will not be used for an SPA.
Assumptions:
Customers will access a restful API to interact with <Service>.
It is expected that customers will create automated scripts, or custom application in their own system to call the API.
Once setup it is not expected that there will be a real person who can provide credentials every time the API is called.
<Service> uses a 3rd party IDP to store and manage users.
3rd part IDP implements OIDC/Oauth and that is how it should be integrated into <Service>
Questions:
What OIDC/OAuth flow should be used in this situation?
What credentials should be provided to the customer? client-id/client-secret or something else?
What tokens can/should be used to communicate information about the "user"? E.g. Who they are/what they can do.
How should those tokens be validated?
Can you point me to any good diagrams/resources that explain this specific use case?
Am I missing anything important in the workflow?
It sounds like these are the requirements, if I am not misunderstanding you. The solution contains not just your own code and is more of a data modelling question than an OAuth one.
R1: Your company provides an API to business partners
R2. Business partners call it from their own applications, which they can develop however they see fit
R3. User authentication will be managed by each business partner, resulting in a unique ID per user
R4. You need to map these user IDs to users + resources in your own system
OAUTH
Partner applications should use the client credentials flow to get an access token to call the API. Each business partner would use a different credential for their set of users.
Using your own IDP to store users does not seem to make sense, since you do not seem to have an authentication relationship with the actual end users.
Access tokens issued to business partners would not be user specific by default. It is possible that a custom claim to identify the user could be included in access tokens - this would have to be developed in a custom manner such as via a custom header, since it is not part of the client credentials flow.
Access tokens would be verified in a standard OAuth manner to identify the partner - and possibly the end user.
DATA
Model users in your own system to have these fields, then store resources (such as orders) mapped against the User ID:
User ID (your generated value)
Partner ID (company the user is from)
External User ID (an ID that is easy for partners to supply)
Typically each partner would also have an entry in one of your database tables that includes a Client ID, name etc.
If you can't include a custom User ID claim in access tokens, partners have to tell you what user they are operating on when they call the API, supplying the external user ID:
POST /users/2569/orders
Your API authorization needs to ensure that calls from Partner A cannot access any resources from Partner B. In the above data you have all the fields you need to enable this.
SUMMARY
So it feels like you need to define the interface for your own APIs, based on how they will be called from the back end of partner apps. Hopefully the above hints help with this.
I'm aware of how OAuth2 and OIDC can use custom scopes and token introspection to secure an URL like this:
/users/me/documents
I can give this URL the documents:view scope and when receiving the token from the authenticated user, I can ask the authorization server if this user has the correct permissions. Then I can use the preferred_username claim or similar to see who /me actually is.
But what if I have a resource which is accessible by multiple users? Let's say a user has documents but they can be viewed by his direct manager. To retrieve the employee's documents as a manager, I'd need to have an url like this:
/users/${userId}/documents
How could I enforce it in a way that only the resource owner and direct manager can view this resource? I don't want everyone to access everyone's documents by knowing the userId. I could grant access as a whole to all users with the manager role, but that's not specific enough.
I'm aware there's the UMA extension where users can grant access to resources on his behalf to other users, but it's not the user who grants permission. It's the system who states in this case that managers can access their employees documents.
Would it make sense to write a custom policy which extracts the ${userId} and performs the check? Or should this not be done by the authorization server at all and be done by the resource server instead? Perhaps a different approach to reach the same goal?
Finer grained authorization like this is done with claims rather than scopes. There may be business rules around which docs a user can see, eg:
A user can access their own docs
An admin has view access to all docs
A manager can view docs for people they manage
In an access token this might be represented by these claims:
userId
role
Claims are often domain specific like this and the preferred option is to add them to tokens during token issuance. At Curity we have some good resources on this topic:
Claims Best Practices
CLAIMS AND AUTHORIZATION
The Authorization Server issues access tokens and then APIs (resource servers) verify the access token and use the token data to apply authorization rules (which are often domain specific) on every single request.
Claims are often used when dynamic behaviour is needed - they are runtime values that derive from the user identity, whereas scopes are fixed design time values. In your example an API might also need to vary SQL to retrieve documents based on the user identity.
There are more complex variations on this theme, such as an API calling a system such as Open Policy Agent, so that documents returned are determined by rules configured by a security administrator. That policy would still involve using claims from the access token though.
EXAMPLE CODE
If it helps, here is some sample code of mine that show the type of approach when enforcing domain specific authorization rules. Typically you need to filter collections and check access to individual items.
I'm implementing my own OpenID Connect provider using Identity Server 4.
I understand, that once issued an access token, clients can use it to obtain claims about the end-user from the userinfo endpoint. Which works great, by the way.
However there are certain use cases where it might be necessary to obtain claims about other users in the system. Think about a user who is head of a department. Clients might want to get email addresses of other users in this department on behalf of this user to notify them about something.
My question is: Is such functionality covered by OpenID Connect or is there a feature in Identity Server 4 to help with this?
I see that I could implement this myself by exposing part of my identity service as just another api protected by the identity server itself. For my use case it would probably be enough to flag certain claims as public for other users, so they can be accessed like any other resource. However there might be some security issues I might be overlooking. Also I would be interested if there was a non-proprietary way to do it, so it could be used by arbitrary clients, and show up in the discovery document.
Any input on this topic would be highly appreciated!