Manage bearer token when we scale on more than one server - OWIN, Katana, AngularJS

In this post we will talk about bearer token authentication and how we should manage this token when our application is running on more than one server -  when we are using OWIN, Katana and AngularJS.

Token Characteristics
First of all let’s see what are the characteristics of bearer token:

• Generate by server
• Contains user claims (what kind of operations a user can do/roles)
• All information that a token contains are encrypted
• Token information can be decrypted only by the machine that created the token
• Expiration date is encrypted in the token itself
• No token information are stored on the server side
• Encryption is safe enough to be used worldwide (Facebook, Google and Twitter are using it) 
• A token can be used by external system only when decryption key is shared
• Easy and cheap to generate tokens

Why?
All this sounds good, but what is happening if we want to go in production. In this case we should be able to scale our backend from one node to 3 or 10 nodes.
Do we need stick connection?... to be able to redirect all the request from the same client to the same instance (because token can be decrypted only by the machine that generate the key)
NO, we don’t need this.

How?
To be able to allow other instances or servers to decrypt and access token information we need to set the machine key. This can be configured directly in the web.config. Once this configuration is done all the encryption/decryption by that application will be use them.

In the system.web section of our configuration file we need to specify the machine key node. We need to specify the validation key, decryption key and what kind of validation and decryption mechanism we want to use.

  <system.web>
    <compilation debug="true" targetFramework="4.5" />
    <httpRuntime targetFramework="4.5" />
    <machineKey validationKey="BDE5239FBD71982481D87D815FA0A65B9F5982D99DFA96E6D92B782E0952D58818B479B19FF6D95263E85B0209297E6858B57D1E0BD3EFECE5E35742D605F2A7"
              decryptionKey="8E8496D7342EA258526CF6177E04EA7D208E359C95E60CD2A462FC062B9E41B3"
              validation="SHA1"
              decryption="AES"/>
  </system.web>

Be aware, don’t use this keys, you should generate your own keys, otherwise "I" will be able to decrypt your token also.
For ISS, the machine key and validation key can be generated easily using ISS features (https://technet.microsoft.com/en-us/library/cc755177(v=ws.10).aspx) or we can use PowerShell (http://support.microsoft.com/kb/2915218#AppendixA)

Conclusion
In conclusion we saw that it is not complicated to 'connect’ multiple application instances to use and access the same token but we need to be able to share the machine key between them.
Another option is to have a dedicate machine that manage and validate token, but this is another story.