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Authorization using tokens in WebAPI

Implementing token based authorization isn’t as hard as it might seem, not with the right tools atleast.
The very brief introduction to Tokens can be derived from the following image;
Token authentication
You Authenticate with a username/password (or something else).
The Server validates the credentials and spits back a token.
The Token is then used for subsequent calls until it expires.

Note:

There are basically three ways of getting a token to the server
1. The URL GET http://tempuri.com/someendpoint?token="".
2. The payload (body) which means you will need to POST to all endpoints (not RESTful)
3. A Header of some sort (generally the Authorization header.
In this post I am going use the Authorization header.
The token type will be Json Web Tokens.
I like JWTokens because they contain everything related to the user, although they do have a significant size to them.

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with HMAC algorithm) or a public/private key pair using RSA.

You can read more on http://jwt.io.
In this post I will also be signing the token using HMAC to secure it from tampering.
What we will be doing is the following;

  • Install needed NuGet packages.
  • Create models to hold a User and the AuthToken.
  • Create a TokenProvider interface and a Json Web Token Provider to create the token.
  • Create a controller to authenticate using Username/Password.
  • Create a Token Authorization Attribute to be used either in webapiconfig.cs or on individual controllers/actions.

Add Nuget Packages.


This could be done without the ThinkTecture one, but I feel like it adds some value.

Create a model to hold the token, this is just a poco containing the token and an expiration time


Next, I’ll create another poco to hold the username/password and Roles associated with the user.

The roles will be assigned on authenticating through the AccountController (which we will do later on).

Create a provider interface and create a JsonWebTokenProvider

The provider will need 2 methods

  • Create a token
  • Validate a token


Interface done, lets move on to the concrete implementation.
There are a few parts we need to handle.
Firstly, we need a few token specific fields namely,

  • Audience – The audience that will be accessing your API
  • Issuer – You..
  • Key – to be used as the HMAC Private Key (Should be unique and safeguarded)
  • SigningCredential – the HMAC signing credential to be used in the header of the JWT –

The signingCredential will be instantiated in the default constructor as you can see in the gist.

Now lets abide by the Interface.
The CreateToken method:
We create a token that is valid for 15 minutes based on the user claims and serialize it to a string.

The ValidateToken method:
We validate a given tokenString based on some validation parameters.

Create AccountController

Here I’ve created 1 method authenticate
Which matches a username/password and creates and returns a token based off that user. The action needs to allow anonymous-access, as we will be adding the Authorization Attribute globally.

We can now authenticate by doing a POST to /account/authenticate?username=admin&password=1235

TokenAuthorizationAttribute

The Authorization Attribute…
Let’s dive right in.
This attribute looks for the Authorization: Bearer {Token} header. If the header is present, and the Token is valid, the Principal gets set and the user is authorized, else a 401 is returned.
I’ve also allowed using the [AllowAnonymous] attribute for the account/authenticate action. and since we are already using claims, we will be able to use the [Authorize] attribute to check roles as well.

Finishing up

All that is left to do, is adding the attribute to WebApiConfig.cs and maybe decorating controller actions with [Authorize(Roles = "Admin")]
The following will make sure that ALL actions (except ones decorated with the [AllowAnonymous] attribute) is secured.

Now you can add [Authorize(Roles = "Admin")] to actions that needs to check roles as well (if needed).

Further more

Alot can be refactored from the code provided, I will leave that up to the reader to decide where and how – I have tried to keep is as simple and as short as possible, therefor I have left out refactorings that I, myself have done.

Remove 'Try it out!' buttons from Swagger-ui

This is a quick way of removing the ‘try it out’ buttons from specific operation types, when using Swagger-ui for documentation

This will be a short one.
When using Swashbuckle to create documentation, you might want to remove the Try it out buttons, maybe all of them, or maybe just the ones on Put on Post operations
Well I’ve created a small script that is injected into swagger-ui through the SwaggerConfig.cs
The following script will remove the TryItOut buttons from all Put and Post operations.

The script is injected through the SwaggerConfig.cs like so

Remember that the .js file needs to be an Embedded Resource else it won’t work.

Adding basic authentication to swashbuckle

Note: This is applies to swashbuckle 5.2.2 and below, will update post for 5.4.0.


On my recent endeavors, I’ve had the pleasure of getting to use “Swagger”, yes it is as swag as it sounds…
Swagger for .Net is thankfully packaged by a guy I only know as “DomainDriven” on github.
The .Net version is called “Swashbuckle”.
I will not go in to adding swashbuckle to your project, the README pretty much says it all.
Lets get back to basic-auth.
According to the swashbuckle docs, to add Basic-Auth to swashbuckle, you need to add the following in the SwaggerConfig.cs file

This adds the “SecurityDefinition” as per the swagger spec.
The SwashBuckler docs finishes the security segment with

NOTE: These only define the schemes and need to be coupled with a corresponding “security” property at the document or operation level to indicate which schemes are required for each operation. To do this, you’ll need to implement a custom IDocumentFilter and/or IOperationFilter to set these properties according to your specific authorization implementation

Which is what I’ll be showing you how to do.

Onwards!

Lets start with the UI.
To remove the APIKey input and replace that with a nice username/password input pair, we need to inject a new index.html.
Note: You can see the base swagger index file here
You can see the entire index.html below
[/learn_more]
What I’ve changed from the original index.html is actually not a whole lot.
I’ve removed everything that had to do with the apikey input and instead added new username and password inputs;
Now all there needs to be done is to inject the new index file into swagger-ui

Now that we have the UI in order, we move on to the actual spec implementation.
To actually live up to the swagger spec, we are still missing the Security Requirement Object on the operations.
According to the spec;

Security Requirement Object
Lists the required security schemes to execute this operation. The object can have multiple security schemes declared in it which are all required (that is, there is a logical AND between the schemes).
The name used for each property MUST correspond to a security scheme declared in the Security Definitions.

Which basically means that we need to add "security": [{"basic": []}] to all of our operations.
This only applies to the code generated by swagger, but how do we implement this through Swashbuckle?
We need to create a class that inherits from the IOperationFilter interface.
And then add the security scheme to all operation.
The security theme is basically just a “basic : []” applied under the security configuration (speaking in pure swagger spec terms).

Now we just need to apply the OperationsFilter in the SwaggerConfig

and that is it, now the “basic” security scheme will be applied to all operations.