In token-based authentication how do tokens get verified? - web-services

I've read numerous token based authentication articles and they typically fail to explain how the server verifies token. I understand that:
User Requests Access with Username / Password
Application validates credentials
Application provides a signed token to the client
Client stores that token and sends it along with every request
Server verifies token and responds with data
But how does step 5 specifically happen?


The token-based authentication terminology can be used in a few contexts so the answer will always depend on the exact question. You did tag your question with JWT (JSON Web Tokens) so I'll answer this by drawing a few assumptions based on that tag.
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.
(emphasis is mine, source: see link above)
This definition sheds some light on your exact question on how a server application verifies a token. It does it, in the case of a JWT, by checking if the associated digital signature is valid; it actually does more than just checking the signature, but this is the most important step.
Digital Signature: A cryptographic method for ascertaining whether or not a digital message or set of documents is genuine, has not been altered or tampered with in transit, and comes from a known sender.
(source: Auth0 Identity Glossary)
You can digitally sign something by applying different algorithms, but this process can be described at a very high-level to consist of the following:
Select a secret that only you (your server) will know about.
Pass the secret and data to be signed to a given algorithm.
The output will consist of a signature that can then be later used to check (if you also know the secret) if some data is exactly equal to the one that originally produced the signature.
In conclusion a server generates a JWT which is signed, distributed to any client application and as long as the server ensures the secret used to sign it is known to no one else it can ensure that the received tokens were not tampered with and were in fact issued by a trusted party.
As mentioned before, the server besides checking the signature can do further validations, usually it will at least also validate that the token is still valid in terms of lifetime. This is recommended because this authentication process that relies purely on having a token, usually referred to as a bearer token, means that if an attacker is able to get hold of a token it can only use it within is configured lifetime. A derived recommendation is that the lifetime of bearer tokens should also be relatively short.


It depends. The token can be a hash of the username the password and a key that the client generates, it can be just random and stored in a db, there is not a unique answer for this

Related

Django Simple JWT logout view [duplicate]

I am using Spring Security OAuth2 and JWT tokens. My question is: How can I revoke a JWT token?
As mentioned here
http://projects.spring.io/spring-security-oauth/docs/oauth2.html, revocation is done by refresh token. But it does not seem to work.

In general the easiest answer would be to say that you cannot revoke a JWT token, but that's simply not true. The honest answer is that the cost of supporting JWT revocation is sufficiently big for not being worth most of the times or plainly reconsider an alternative to JWT.
Having said that, in some scenarios you might need both JWT and immediate token revocation so lets go through what it would take, but first we'll cover some concepts.
JWT (Learn JSON Web Tokens) just specifies a token format, this revocation problem would also apply to any format used in what's usually known as a self-contained or by-value token. I like the latter terminology, because it makes a good contrast with by-reference tokens.
by-value token - associated information, including token lifetime, is contained in the token itself and the information can be verified as originating from a trusted source (digital signatures to the rescue)
by-reference token - associated information is kept on server-side storage that is then obtained using the token value as the key; being server-side storage the associated information is implicitly trusted
Before the JWT Big Bang we already dealt with tokens in our authentication systems; it was common for an application to create a session identifier upon user login that would then be used so that the user did not had to repeat the login process each time. These session identifiers were used as key indexes for server-side storage and if this sounds similar to something you recently read, you're right, this indeed classifies as a by-reference token.
Using the same analogy, understanding revocation for by-reference tokens is trivial; we just delete the server-side storage mapped to that key and the next time the key is provided it will be invalid.
For by-value tokens we just need to implement the opposite. When you request the revocation of the token you store something that allows you to uniquely identify that token so that next time you receive it you can additionally check if it was revoked. If you're already thinking that something like this will not scale, have in mind that you only need to store the data until the time the token would expire and in most cases you could probably just store an hash of the token so it would always be something of a known size.
As a last note and to center this on OAuth 2.0, the revocation of by-value access tokens is currently not standardized. Nonetheless, the OAuth 2.0 Token revocation specifically states that it can still be achieved as long as both the authorization server and resource server agree to a custom way of handling this:
In the former case (self-contained tokens), some (currently non-standardized) backend interaction between the authorization server and the resource server may be used when immediate access token revocation is desired.
If you control both the authorization server and resource server this is very easy to achieve. On the other hand if you delegate the authorization server role to a cloud provider like Auth0 or a third-party component like Spring OAuth 2.0 you most likely need to approach things differently as you'll probably only get what's already standardized.
An interesting reference
This article explain a another way to do that: Blacklist JWT
It contains some interesting pratices and pattern followed by RFC7523

The JWT cann't be revoked.
But here is the a alternative solution called as JWT old for new exchange schema.
Because we can’t invalidate the issued token before expire time, we always use short-time token, such as 30 minute.
When the token expired, we use the old token exchange a new token. The critical point is one old token can exchange one new token only.
In center auth server, we maintain a table like this:
table auth_tokens(
user_id,
jwt_hash,
expire
)
user_id contained in JWT string.
jwt_hash is a hash value of whole JWT string,Such as SHA256.
expire field is optional.
The following is work flow:
User request the login API with username and password, the auth server issue one token, and register the token ( add one row in the table. )
When the token expired, user request the exchange API with the old token. Firstly the auth server validate the old token as normal except expire checking, then create the token hash value, then lookup above table by user id:
If found record and user_id and jwt_hash is match, then issue new token and update the table.
If found record, but user_id and jwt_hash is not match , it means someone has use the token exchanged new token before. The token be hacked, delete records by user_id and response with alert information.
if not found record, user need login again or only input password.
when use changed the password or login out, delete record by user id.
To use token continuously ,both legal user and hacker need exchange new token continuously, but only one can succeed, when one fails, both need to login again at next exchange time.
So if hacker got the token, it can be used for a short time, but can't exchange for a new one if a legal user exchanged new one next time, because the token validity period is short. It is more secure this way.
If there is no hacker, normal user also need exchange new token periodically ,such as every 30 minutes, this is just like login automatically. The extra load is not high and we can adjust expire time for our application.
source: http://www.jianshu.com/p/b11accc40ba7

This doesn't exactly answer you question in regards to the Spring framework, but here's an article that talks about why if you need the ability to revoke JWT's, you might not want to go with JWT's in the first place, and instead use regular, opaque Bearer tokens.
https://www.dinochiesa.net/?p=1388

One way to revoke a JWT is by leveraging a distributed event system that notifies services when refresh tokens have been revoked. The identity provider broadcasts an event when a refresh token is revoked and other backends/services listen for the event. When an event is received the backends/services update a local cache that maintains a set of users whose refresh tokens have been revoked.
This cache is then checked whenever a JWT is verified to determine if the JWT should be revoked or not. This is all based on the duration of JWTs and expiration instant of individual JWTs.
This article, Revoking JWTs, illustrates this concept and has a sample app on Github.

For Googlers:
If you implement pure stateless authentication there is no way to revoke the token as the token itself is the sole source of truth
If you save a list of revoked token IDs on the server and check every request against the list, then it is essentially a variant of stateful authentication
OAuth2 providers like Cognito provides a way to "sign out" a user, however, it only really revokes refresh token, which is usually long-lived and could be used multiple times to generate new access tokens thus has to be revoked; the existing access tokens are still valid until they expire

What about storing the JWT token and referencing it to the user in the database? By extending the Guards/Security Systems in your backend application with an additional DB join after performing the JWT comparison, you would be able to practically 'revoke' it by removing or soft-deleting it from the DB.

In general, the answer about tokens by reference vs. tokens by value has nailed it. For those that stumble upon this space in future.
How to implement revocation on RS side:
TL;DR:
Take a cache or db that is visible to all your backend service instances that are verifying tokens. When a new token arrives for revocation, if it's a valid one, (i.e. verifies against your jwt verification algo), take the exp and jti claims, and save jti to cache until exp is reached. Then expire jti in cache once unixNow becomes > exp.
Then on authorization on other endpoints, you check everytime if a given jti is matching something in this cache, and if yes, you error with 403 saying token revoked. Once it expires, regular Token Expired error kicks in from your verification algo.
P.S. By saving only jti in cache, you make this data useless to anyone since it's just a unique token identifier.

The best solution for JWT revocation, is short exp window, refresh and keeping issued JWT tokens in a shared nearline cache. With Redis for example, this is particularly easy as you can set the cache key as the token itself (or a hash of the token), and specify expiry so that the tokens get automatically evicted.

I found one way of resolving the issue, How to expire already generated existing JWT token using Java?
In this case, we need to use any DB or in-memory where,
Step 1: As soon as the token is generated for the first time for a user, store it in a db with the token and it's "issuedAt()" time.
I stored it in DB in this JSON format,
Ex: {"username" : "username",
"token" : "token",
"issuedAt" : "issuedAt" }
Step 2: Once you get a web service request for the same user with a token to validate, fetch "issuedAt()" timestamp from the token and compare it with stored(DB/in-memory) issued timestamp.
Step 3: If stored issued timestamp is new (using after()/before() method) then return that the token is invalid (in this case we are not actually expiring the token but we are stop giving access on that token).
This is how I resolved the issue.

JWT Tokens in Django Rest Framework

I am building a Django Rest Framework API which is using JWT authentication. I had created access tokens and refresh tokens and sent them to users.
I also have a refresh token endpoint that will take old refresh token and generate new pair of tokens and send to user.
I have doubt in its behavior related part. Currently what I can see that whenever I create new pair of access and refresh token using previous refresh token, the old access token is also working and new one is also working.
However once when I was using OAuth2.0 (in different case), I observed that in that case the old access token won't work if we had created new refreshed tokens.
But in case of my implementation of JWT in DRF this thing won't happens. I am not storing token in database.
So I want to know that is this any implementation specific problem or is it the property of JWT only, and if it is property then please share some details over it with me.
Thanks.

According to JWT introduction:
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 the HMAC algorithm) or a public/private key pair using RSA or ECDSA.
One of the value, that you can encode is 'exp' which states for expiration date. That's why your old tokens do not expire, cause they expiration date is still valid, and any other claims didn't change. Idea behind the 'refresh' token, is to provide new tokens with bigger exp value. Saying other way, you should not expect that the authorization will fail now, as the old token is still correct one.
As well you store nothing in the database (about this I also suggest to read answer provided by #sdoxsee

AWS Cognito - verify token using JWT vs cognito.getUser SDK

I am using the following doc by AWS for verifying the incoming token with Cognito to verify the user in cognito pool:
https://docs.aws.amazon.com/cognito/latest/developerguide/amazon-cognito-user-pools-using-tokens-verifying-a-jwt.html
Now I also need to verify one of the custom attributes (email) of that user. (Basically this is to mitigate a case where some user can change their email-id in the API payload to access someone else's details).
The Cognito SDK I found to do this was this : https://docs.aws.amazon.com/cognito-user-identity-pools/latest/APIReference/API_GetUser.html
It works just fine, however this led me to a question :
Since I'm sending access token in this SDK, do I need to use the former jwt-based token verification as well? Because this SDK also handles the case where token is invalid/expired and sends error codes accordingly. Is there something I'm missing which the former case handles and the latter one doesn't ?

Short answer: no, you can ignore the contents of the JWT.
Longer answer: JWT tokens provide a fast way to verify that a user has been authenticated, without the need to check a database or external service. This can be very important in a high-volume application.
However, they have several limitations:
A JWT token is issued with an expiration timestamp. If you rely on the JWT, you do not have a way to forcibly log-out a user until that timestamp expires.
To be secure, your JWT token must be signed using an asymmetric keypair (I mention this simply because a lot of people have implemented their own identity servers incorrectly; Cognito does it right).
The claims that are in the token (and are signed by the identity server) may not be sufficient for your needs. Best practice is to minimize the size of the token, and iirc Cognito follows this practice by only including the user attributes that are directly tied to authentication.
If any of these limitations apply to a particular use-case (and it sounds like the third applies to you), then you'll have to make that external service call to the identity server. And if you do that, and the server reports authentication status, then there's no need to pay attention to the token.

Is there any point in encrypting identity tokens?

I am developing a restful web service and it needs securing. I am doing this using a token system where the client passes a token unique to them via the request header. The service has to be called via HTTPS.
I have seen a few articles which encrypt the token but is there any real benefit to doing this as the token would naturally be encrypted by HTTPS anyway....?
After re-reading the above I realise that it is not entirely clear what I meant...
The articles I have seen give the client a pre-encrypted Token which was encrypted with a public key. They then decrypt this token on receipt of the request and check it against the stored unencrypted token. To me it seems that this has no benefit over simply giving the client an unencrypted token and saving on the whole decryption overhead....

I think it's a broad question and the answer will depend on your requirements. But, in most of cases, you won't need cryptography in your identity tokens.
Identity tokens (used to perform authentication) can be opaque (tokens that reveal no details other than the value itself, like a random string) or can be self-contained (like JSON Web Tokens).
For more details, see below:
Random string
A token can be issued by generating a random string and persisting it to a database with an expiration date and with a user identifier associated to it.
JSON Web Tokens (JWT)
Defined by the RFC 7519, it's a standard method for representing claims securely between two parties. JWT is a self-contained token and enables you to store a user identifier, an expiration date and whatever you want (but don't store passwords) in a payload, which is a JSON encoded as Base64. The payload can be decoded and read by the client.
With JWT, you can perform stateless authentication, that is, you won't need to persist JWT tokens if you don't need to track them. Just check the integrity of the token by verifying its signature on the server side.
Although, by persisting the tokens, you will have the possibility of invalidating and revoking the access of them. To keep the track of JWT tokens, instead of persisting the whole token, you could persist the token identifier (the jti claim) and some metadata (the user you issued the token for, the expiration date, etc) if you need. To find some great resources to work with JWT, have a look at http://jwt.io.
For tokens with cryptography, have a look at JSON Web Encryption (JWE), defined in the RFC 7516. Use JWE when you need confidentiality, so the client will need a key to decrypt the content of the token.

Verify OAuth2 login information without calling authorization server on every request

Actors
Front-end (fat client-side Javascript application) which has Facebook access token.
Back-end which 100% relies on OAuth2 authentication. All requests need to be authenticated via Facebook.
To mutate user data on the back-end, I require user to be logged in via Facebook. Ideally, with every request, I would know the Facebook's user ID (the one that graph.facebook.com/me provides).
Question 1
Is there a way to get whatever graph.facebook.com/me returns to be signed, so I don't have to call Facebook to verify it with every request, nor store state in my backend?
Situation 2
If the answer to Question 1 is "no", it means I have to invent my own. I am thinking of the following:
The user sends the access token to the backend.
Backend calls token debug API, signs the result with my key, and sends back to the client.
Every time client does a request, it includes the previously-included blob.
Upon every incoming request to the backend, it verifies the signature, which, if matches, means that the request wasn't tampered with and I can trust it is coming from the previously-verified token.
Question 2
If I employ this scheme (sign the answer from Facebook and send it upon every request), how can I safely implement this? Are there resources I could read up which would tell me:
Things to be cautious about with this scheme.
Which signature algorithm to use, how to safely verify the signatures.
How to avoid common types of attacks and stupid mistakes.
Thanks!

It's not really clear what exactly you want to do, but I think you should have a look at the docs at
https://developers.facebook.com/docs/graph-api/securing-requests
Quote:
Graph API calls can be made from clients or from your server on behalf of clients. Calls from a server can be better secured by adding a parameter called appsecret_proof.
Access tokens are portable. It's possible to take an access token generated on a client by Facebook's SDK, send it to a server and then make calls from that server on behalf of the person. An access token can also be stolen by malicious software on a person's computer or a man in the middle attack. Then that access token can be used from an entirely different system that's not the client and not your server, generating spam or stealing data.
You can prevent this by adding the appsecret_proof parameter to every API call from a server and enabling the setting to require proof on all calls. This prevents bad guys from making API calls with your access tokens from their servers. If you're using the official PHP SDK, the appsecret_proof parameter is automatically added.