I am looking at implemented Cognito for user login and would like to understand the process of validating JWT's a little better.
The application in question is on asp.net 4.5 MVC and not related to .NET Core. The only information on AWS Cognito I can find online relates to .NET core.
I understand the meaning of each token type as documented here:
https://docs.aws.amazon.com/cognito/latest/developerguide/amazon-cognito-user-pools-using-tokens-with-identity-providers.html#amazon-cognito-user-pools-using-the-id-token
I also understand the required steps in validating a JWT:
https://docs.aws.amazon.com/cognito/latest/developerguide/amazon-cognito-user-pools-using-tokens-verifying-a-jwt.html
My question is which JWT needs to be validated and at what stage?
Example 1.
A user logs in, once logged in they are returned with an Access, ID and Refresh token.
Do all of the tokens need to be validated at this point or just the Access token?
Is the refresh token only validated before trying to use it (in order to gain new access and ID tokens)?
OR should all tokens be validated on any authorised content request?
What tokens should be stored in the FormsAuthentication Cookie for use later? We are using the standard [Authorize] pattern in asp.net.
Question: Do all of the tokens need to be validated at this point or just the Access token?
Answer:
Validation is always done on Access token only.
Refresh token itself need not be validated. It is merely used for the purpose of obtaining fresh set of ID token and Access token.
Question: What tokens should be stored in the FormsAuthentication Cookie for use later?
Answer: This is specific to implementation. There is no rule on what token must be saved.
If the requirement is to just know the user's email or phone number, then just the ID token can be saved.
If the requirement is to allow one-time access for up an hour for the user,
then storing just the access token is sufficient.
If the requirement is to allow user to access the resource for up to 30 days, without being prompted for password, then refresh token must be saved.
The recommended approach is to validate the access token as it includes both authentication and authorization. You should be validating access token prior to providing access to protected resources.
The id token contains claims (information) of the authenticated user. It can be used for verification as well but there is more power in using access tokens as you can create scopes to define permissions and roles. Access token is also the input to many of Cognito APIs user operations.
AWS Cognito follows OpenID Connect Protocol which is built on top of Oauth2 for which these terminologies originate from.
The refresh token is a long lived token to retrieve newer short lived tokens (id token, access token). Currently with Cognito's implementation, shorter lived tokens expire every 1 hour and refresh tokens are configurable in the user pool. In the case where a refresh token becomes invalid/expired, attempts to retrieve newer short lived tokens will fail therefore you do not need to validate refresh token yourself.
You can store the refresh token (in some sort of session) to assist with the retrieval of new access, id tokens without re-authentication. You can also store the access token so that the refresh token is used only once per hour (when the access token expires) to prevent issuance of unnecessary tokens and round-trips to Cognito. The id token storage is really up to your use case, if you were interested in keeping the user claims (user information stored in the JWT of id token).
I understand that access tokens are not saved at the server side (usually) and are just verified using some key an algorithm. However, it seems that the normal behavior is to save a refresh token in the server side(i.e:database) and compare it with the user's when the user is trying to refresh their access token. My question is why not just verify the refresh token the same way the access token was verified?
It is generally more secure if a token is an ID that is validated against a database, as this allows the token to be revoked at any time (by removing it from the database or marking it as invalid).
Self-validating tokens, such as JWTs, cannot be revoked (without using a database, which defeats most of the benefits of using self-validating tokens) - they can only expire. Therefore, they should have a short expiry time. The benefit of self-validating tokens is not only performance, but also eliminating dependencies, as the resource server does not need to connect to a database owned by the authorization server. Instead it can simply validate the tokens by itself, using a trusted public key.
Using a database is also easier to implement, as most web apps already have one anyway, and self-validating tokens are easy to do wrong (there are many JWT libraries out there that have flaws or bad defaults).
The refresh token is only used to request a new access token, so performance is not important. The request is sent to the authorization server, which "owns" any authorization-related database(s), so it does not add any unwanted dependencies.
Note that access tokens do not have to be self-validating tokens. It is perfectly fine if they are also simply IDs validated against a database. The separation between access token and refresh token only makes it possible to choose an implementation using self-validating access tokens.
I am developing an OAuth2.0 Server. What should be the format of refresh token and what encryption algo should be used for encryption?
OAuth 2.0 does not enforce any restrictions regarding token formats or encryption. Encryption is completely disregarded in the spec, as communication is supposed to be secured with TLS.
Also - don't implement yourself if you don't really have to. Choose an open source library or even a vendor product if your funding permits it.
That being said, take a look at the JWT RFC. That's the format most people use. You can also consider no format at all and just work with opaque strings, and then implement token introspection in your Authorization server.
As to encryption - anything goes. Most implementations out there support at the very least HS256, RS256 and ES256 for signing JWT tokens. In most real world scenarios you don't need to encrypt the token, a signature is enough.
After struggling for sometime, I figured it out. There are two approaches
Either put everything that you need to construct access token (apart from things that can be derived/calculated directly) in refresh token and encrypt it with global or tenant level symmetric key
Benefits:
a. No storage required
b. Better performance as No contact with DB is required. It is just decryption and creation of access token
Issues/shortcomings
a. No way to keep track of refresh tokens issued.
b. No way to invalidate the issued refresh tokens.
Storing attributes related to refresh token in DB and in response of OAuth Server, returning encrypted refresh token ID. Attributes that might be stored in DB are
ID || Expiry || Count of Token || Subject || Client ID || Custom Attributes (If required)
There can be other attributes as well which we implemented but this must give a bit of idea to people who want to implement their own Refresh Token flow
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.
I am creating an Oath 2.0 system on my server allowing users to log into their account on my server from the app without having to give the username and password to the app itself. Which as I understand is the purpose of Oath, and it seems to work pretty well, the system is built on compliance with all Oath 2.0 specifications and is fully functional. But what I don't understand is why I have to have tokens expire... I mean I provide a refresh uri and they can easily at any time and at no cost renew the token (or get a new valid one). I dont see any purpose in this, why not just make the token never expire. I don't see the security benefits or any purpose for that matter for token expiration. Can someone explain to me why I have to have my tokens expire and why they can't just be good indefinitely?
In a word, for more safe.
In your question, you said at no cost renew the token, actually, when you refresh token, you need to authenticate with the authorization server(provide your client credential). So refresh token is not equal with access token. It can not give you the access to resource.
Why have token expire?
As OAuth 2.0 Threat Model and Security Considerations says:
3.1.2. Limited Access Token Lifetime
The protocol parameter "expires_in" allows an authorization server
(based on its policies or on behalf of the end user) to limit the
lifetime of an access token and to pass this information to the
client. This mechanism can be used to issue short-lived tokens to
OAuth clients that the authorization server deems less secure, or
where sending tokens over non-secure channels.
5.1.5.2. Determine Expiration Time
Tokens should generally expire after a reasonable duration. This
complements and strengthens other security measures (such as
signatures) and reduces the impact of all kinds of token leaks.
Depending on the risk associated with token leakage, tokens may
expire after a few minutes (e.g., for payment transactions) or stay
valid for hours (e.g., read access to contacts).
I found another use for it. When I store a token in my database at every login. If someone no longer uses a device or deletes their token (uninstalls an app or clears a cache) for any reason without properly "logging out" (logging out removes it from the database). Then there is a token stored on the database that will never be used again. After a while this becomes cumbersome taking up valuable space on the database and slowing down query executions for unused tokens. With token expirations I can run a cron job to scan the database for expired tokens every 15 minutes or so and remove them. Having to refresh tokens does put some strain on the server and the client but not as much as having potentially millions of unused tokens.