Levels of Access Control through Keycloak Part 3: Access Control Through Roles and Tokens

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This is part 3 of a 4-part series on Keycloak. For part 1, click here and for part 2, click here.

In one of the previous guides, we covered how tokens generated by Keycloak have some very specific pieces of information (claims) due to its support for OpenID Connect. However, the token also contains some non-standard claims, such as preferred_username. Let's generate a token, examine it, and see what else is in there. Use one of the methods discussed in the previous guides to generate a token. I'm just going to put a decoded token payload in here:

{
"exp": 1596517043,
"iat": 1596481043,
"jti": "24690fd3-bf00-450f-8937-1893cea8bf8a",
"iss": "http://localhost:8080/auth/realms/test",
"aud": "account",
"sub": "f33d74d4-a5ed-4da0-817c-503e75a81465",
"typ": "Bearer",
"azp": "my-test-client",
"session_state": "f8530352-29b3-47f0-bfb5-914bc8b6536e",
"acr": "1",
"allowed-origins": [
"/*"
],
"realm_access": {
"roles": [
"offline_access",
"uma_authorization"
]
},
"resource_access": {
"account": {
"roles": [
"manage-account",
"manage-account-links",
"view-profile"
]
}
},
"scope": "email profile",
"email_verified": false,
"preferred_username": "admin"
}

One of the very first things to observe is the realm_access claim. In the value, you can see the actual roles assigned to the user admin. Let's create a new role, assign it to this user, and regenerate the token. To create a new role, log-in to the Keycloak Administration Console, click on Roles from the navigation and then click on Add Role:

For the new role, you just need to provide the Role Name. I'm naming it my-new-role:

Now let’s navigate to Users, search for admin, open it, click on Role Mappings. From there, select the new role we created i.e my-new-role, and click on Add Selected.

Regenerate the token through one of the methods in the previous guides and inspect its payload:

{
"exp": 1596777325,
"iat": 1596741325,
"jti": "241d782b-f701-435d-b107-274662950bd0",
"iss": "http://localhost:8080/auth/realms/test",
"aud": "account",
"sub": "f33d74d4-a5ed-4da0-817c-503e75a81465",
"typ": "Bearer",
"azp": "my-test-client",
"session_state": "d8ac57d1-6909-4fa1-81fb-a9368418a87e",
"acr": "1",
"allowed-origins": [
"http://localhost"
],
"realm_access": {
"roles": [
"my-new-role",
"offline_access",
"uma_authorization"
]
},
"resource_access": {
"account": {
"roles": [
"manage-account",
"manage-account-links",
"view-profile"
]
}
},
"scope": "email profile",
"email_verified": false,
"preferred_username": "admin"
}

The realm_access claim would contain the new role we created. Similarly consider the resource_access claim. It contains the client roles assigned to the user admin. A client role is a role that is only relevant to a client in Keycloak. They can be viewed in the Administration Console by opening the client configuration and clicking on Roles:

Click on Add Role to define a new role for this client. Like before, a role only requires a name:

Now, we assign this role to the user admin in a similar fashion. Navigate to users, open up admin, click on Role Mappings, in the drop-down against Client Roles, search for the client in which we created the role by typing my-test-client. It should appear in the list. Select it. Another roles list appears, select our newly created role from that list and click on Add Selected:

Regenerate the token through one of the methods in the previous guides and inspect its payload:

{
"exp": 1596778012,
"iat": 1596742012,
"jti": "04b7a32a-a15a-45dc-95ef-4c47cbc23746",
"iss": "http://localhost:8080/auth/realms/test",
"aud": "account",
"sub": "f33d74d4-a5ed-4da0-817c-503e75a81465",
"typ": "Bearer",
"azp": "my-test-client",
"session_state": "ae62d1f2-2315-4c58-9cec-1337421b592d",
"acr": "1",
"allowed-origins": [
"http://localhost"
],
"realm_access": {
"roles": [
"my-new-role",
"offline_access",
"uma_authorization"
]
},
"resource_access": {
"my-test-client": {
"roles": [
"my-new-client-role"
]
},
"account": {
"roles": [
"manage-account",
"manage-account-links",
"view-profile"
]
}
},
"scope": "email profile",
"email_verified": false,
"preferred_username": "admin"
}

As you can see, the newly created client role appears in resource_access claim against the client name.

You get the same token in your service or app, and if you want, you can leverage this information to restrict access to an API to certain role(s). Let’s do this in our original example of the /v1/self API. We'd have to modify the SelfApi on_get function as follows:

class SelfApi(object):  def on_get(self, req, resp):
if req.auth is None:
raise falcon.HTTPUnauthorized('Unauthorized', 'Bearer token not provided')
try:
token = req.auth.split(' ')[1]
claims = client.validate_jwt(token, options={'verify_aud': False})
# We check for the presence of roles in the realm_access
# claims
if 'my-new-role' in claims['realm_access']['roles']:
resp.body = dumps(get_user(claims))
resp.status = falcon.HTTP_200
return
# if the role isn't present, we need ro return 403
raise falcon.HTTPForbidden('Forbidden', 'User does not have the required role')
except falcon.HTTPForbidden:
raise
except Exception as e:
raise falcon.HTTPUnauthorized('Unauthorized', e.args[0])

Modify our original example code as above and run it. Generate a new token through admin and do a GET through curl like below:

curl -H "Authorization: Bearer <TOKEN>" http://localhost:1234/v1/self

This would yield:

{
"id": "f33d74d4-a5ed-4da0-817c-503e75a81465",
"username": "admin"
}

Now remove the role from the user admin by going into Role Mappings, selecting my-new-role from the Assigned Roles and clicking on Remove Selected. Regenerate the token and perform the above GET request again. You'd get:

{
"title": "Forbidden",
"description": "User does not have the required role"
}

You can similarly pull this off using client roles specified in resource_access too.

There are certain scenarios in which you might want additional information in the token e.g. groups assignment or you might want the roles but against another key instead of realm_access. Fortunately, Keycloak lets you do that. For example, if you want to add the groups that a user is part of to the token, open up the client against which the token is generated from the Administration Console and click on Mappers:

A mapper is a configuration that maps a piece of information to a key or property in the token. There are a bunch of built-in mappers that already come with Keycloak but for our use case, let’s create a new one by clicking on Create.

In the create dialog, write down a name for the mapper and from the Mapper Type select Group Membership. In the Token Claim Name specify the name of the key against which you'd want the groups to be specified. Additionally, this mapper can modify the payload at a bunch of places, including the access token. For now, let's just make sure that the button for Add to access token is ON.

Let’s also create a group and assign it to our admin user to view the effects. For that, click on Groups from the navigation. Click on New.

Provide a name for the new group and click on Save. I'm going to use my-new-group:

To add the admin user to this group, click on Users from the navigation, search for the admin user and open its settings. Click on Groups. From the Available Groups list, click on the group we just created i.e. my-new-group and then click on Join:

Now, if we regenerate the token, the payload would be something like this:

{
"exp": 1596828991,
"iat": 1596792991,
"jti": "ea19a7ca-b72a-4b13-abc6-d0b8cc66db77",
"iss": "http://localhost:8080/auth/realms/test",
"aud": "account",
"sub": "f33d74d4-a5ed-4da0-817c-503e75a81465",
"typ": "Bearer",
"azp": "my-test-client",
"session_state": "65b34a44-2413-4db5-9daf-c870b2bed9c3",
"acr": "1",
"allowed-origins": [
"/*"
],
"realm_access": {
"roles": [
"offline_access",
"uma_authorization"
]
},
"resource_access": {
"my-test-client": {
"roles": [
"my-new-client-role"
]
},
"account": {
"roles": [
"manage-account",
"manage-account-links",
"view-profile"
]
}
},
"scope": "email profile",
"email_verified": false,
"groups": [
"my-new-group"
],
"preferred_username": "admin"
}

As you can see, the groups that the user admin is part of now appear against a claim called groups in the token. Once a mapper is configured, your application can utilize the new claim in the token to implement group-based access control.

Conclusion

Apart from the standard OpenID Connect claims, Keycloak also includes some non-standard claims in the token and also provides the flexibility to the user to include some more non-standard claims as needed. This feature can be utilized to implement access control policies based on the information we include in the token. In the next part, I will demonstrate the usage of this feature to integrate Keycloak with 3rd party open-source solutions.

Code Mechanic and Deployment Plumber, Curious for Details

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