1. Demo Setup
2. Features
3. Goals and methodology
4. Reflection and what I'd do differently

Firstly, from the project root build the solution to have npm setup the required modules.

$ dotnet build

The identity and main api databases need to be generated prior to launch. Migrations are packaged with the repository and do not need to be generated.

$ cd src/PermissionServerDemo.Identity
$ dotnet ef database update

$ cd src/PermissionServerDemo.Api
$ dotnet ef database update

The database has a seeded default user with the following email & password combination:

username: admin@mydomain.com
password: password

the tracked .vscode folder contains json files to launch all 3 projects at once. Navigate to the debug tab in vscode and select the "Api, Idp, and Client" selection, then click on the Run button. Your browser will automatically launch a window and begin serving the Angular client.

Email configuration is stored in user secrets and injected via the IOptions interface. To set the email configuration, sign up for a free account with SendGrid and enter your credentials into user secrets. This is not necessary for the main demo. Only if you want to test out registration.

$ cd src/PermissionServerDemo.Identity
$ dotnet user-secrets init
$ dotnet user-secrets set "Email:SendGridUser" "<your_username>"
$ dotnet user-secrets set "Email:SendGridKey" "<your_key>"

1. Fully typesafe permissions to be used throughout the application. These are stored in a class library so both the API and the IDP can have compile-time safety. These work with migrations for updates and tweaks over the life of an application's development cycle.
2. Custom roles with specific permissions that can be defined by individual tenants. Global defaults are configured as a suggested default and for initial users.
3. Local and remote authorization using these permissions and gRPC. IDP controller methods can be protected exactly like the API controller methods can be.
4. Immediate updating of permissions using the above system. The second a permission is updated, it will be reflected throughout the system.
5. Account management, email confirmation (not required to be setup for the main demo), and tenant invitation management using a placeholder implementation. These are not a part of the main demo, but can be accessed if desired.

1. Multitenancy with data segregated by an id in each record.
2. Typesafe authorization guards on controllers or controller methods.

1. A GUI that showcases the backend identity system's customization and immediate reflection of authorization changes.

This project has three main goals in order of least to greatest difficulty

This is relatively straightforward. Using IdentityServer, the three projects are separated cleanly with JWTs issued by the identity provider. These JWTs are used solely as authentication and not authorization in the expected way authentication JWTs are used.

Initially I wanted to try a database-per-tenant approach as this is the more difficult method. I was able to get this working in this version of EF Core, however after further research and experimentation I decided this approach isn't worth it. Specifically, the management of tenant creation becomes unwieldy as asynchronous migration and database creation must take place and then users updated when this is done. Among other reasons, this was scrapped in favor of simpler data segregation via a tenant id in each record of the db. This is achieved very simply by EF Core QueryFilters and is not complex at all.

The multitenancy aspect is handled almost entirely by the client. It implements its own portal where a user selects from their lists of available tenants. Handling this in the client as opposed to setting this on the identity side means that it is easier and faster for the user to work with multiple tenants, accessing data in one and then quickly moving to another. The client uses the selected tenant's GUID when making calls to the API. This means no state is held by the API and there is no conflict of refreshing when the tenant id is stored in the JWT.

Permissions is really the largest problem here. When it boils down to it, there are really three possible ways to handle updating of permissions.

The easiest of the 3 methods, the basis of this is to put permissions information (or, at least, roles) into the JWT and have a very short refresh timer (< 10 minutes) so that when a user's access is changed, it will be updated eventually. Similarly I have seen systems where the tenant id is stored in the JWT. The downside of storing the tenantId as a claim (like Azure or other companies do, although their systems fit their requirements) is that you will have to log your user in and out if they switch tenants. I don't believe there is built-in functionality to "soft-relog" a user currently, so while it would sound great to simply re-issue the token without prompting the user when they select a tenant to change, I don't believe it can be done, at least not without lots of custom complex code.

This is how Auth0 does it. Regardless of the arguments against tracking jwts, many companies do it for revocation anyway. The downside is a lot of custom code server and client-side that goes against a standard that may have major security implications. Basically, a lot of work and kind of hacky (though pragmatic).

This is how some companies do it, using services like OPA (basically json XACML that's very fast for those with prior knowledge). You have a remote server authorize requests that are protected. The API holds the application logic and when the user calls the api, if that endpoint is protected, a network request with the necessary information is sent over to an identity server that decides whether that user is able to do something or not. This is the approach I chose. It isn't for everyone but I wanted to try this. I chose to use gRPC to make authorization validation network calls for each protected endpoint using custom attributes.
Pros

1. Immediate updating of permissions.
2. The API needs to know nothing about users, tenants, or anything else. Just the main application logic.
   

Cons

1. Network traffic/latency, partially mitigated by using gRPC calls. There is simply no way around this and IMO it is worth it if you need security.
2. Coupling between the identity provider and the API, however it is quite workable from a developer standpoint because gRPC protos provide a very nice contractual understanding between servers and only one or two proto files are needed. Permissions, if stored as an Enum like here, can be stored in a shared library so no magical strings are used and compile-time safety is kept.

There are tons of different ways to approach authorization whether it be claims, roles, or policies including both. I chose to map tables to two enum values representing Permissions and PermissionCategories (used for sorting on the front end). On migration, they are updated from the enums in code. There are many different approaches. Using an enum decorated with the [Flags] attribute is the most performant way if you want to model finely-grained permissions and you need less than 64 (the max if using long). I chose not to do this because if you need less than 64, this method is very well understood and many examples exist of how to make such a system. This is a bit harder but also allows for a larger amount of permissions.

Some people also go about making a CRUD-based system with these flags. Something like Aircraft - 0101 where each bit is a letter of CRUD. My problem with this is that realistically not all protected things are resources. Not all operations fall under CRUD. However, realistically this section is what needs to be customized most. As the creators of PolicyServer and IdentityServer have pointed out, authentication is easy to make for everyone, authorization is a very case-by-case basis where a custom system is needed and the requirements may widely vary.

Regardless, using the existing authorization within ASP.NET Core and gRPC leads to a fast, reusable and low-code solution.

The last feature of this project is the ability for admins to make their own roles and assign them to their users. Global roles are provided as suggested defaults. This is likely overkill for most projects but is another interesting feature for more complicated designs.

Seeing as .NET is moving away from IdentityServer, something like Keycloak or another open-source authentication library would be better. A more fleshed out system for tracking and managing permissions can be done, specifically it was not possible to do some checks on permissions and existing records during migration at the time, but it was planned to allow this when I checked.