I am currently attempting to implement auth into my API and am puzzled by the concept of refresh tokens. I understand they are for generating new access tokens upon their expiration, however I am unsure as to what payload they are meant to carry and how they are meant to be stored in the DB.
Several sources have implemented refresh tokens using the same payload as the access tokens (i.e a userId). Others have implemented a session system whereby a session object is serialized and checked upon validation.
My main confusion regards the validation and invalidation of refresh tokens. Are refresh tokens meant to be stored in the DB alongside the user, such that you can check that it is valid (and not being reused)? If so, should it be deleted from the DB when a new refresh token is generated? If this is the case, how do you allow for multiple sessions across several clients? It seems wasteful to store all past refresh tokens or session objects in the DB, particularly if the expiration time of the access token is short.
Apologies for the somewhat rambling question. This topic is one I'm struggling to get a grip of so any help would be much appreciated.
First please understand the importance of JWT token , they are meant to verify the integrity of the user i.e. genuine user.
For this purpose access token are generated and verified at each request to check weather the authentic user is making that request and also these token have expiring time based on your requirement and to refresh them refresh token are used. now lets say your token have very short TTL and you make request to refresh your token with each request of refreshing these token your server has to access DB and refresh the token , if you have store serialized object in token then it would add another business logic to deserialize and check for the Userid.
therefore the you should store minimum information in these token access token as well as refresh token , and this refresh token you should store along side user with minimum information.
Related
I am making an application that generates refresh token that implements JWT token authentication, and I am not sure what format should I use to identify the refresh token. Initially, I thought that it should be in JWT token format, but based on my googling, it seems like it is represented in a UUID or hashed format? Just wondering whether I should make it JWT token format, or it does not matter in the case of refresh token?
Thanks in advance for helping to clarify this issue.
From here https://developer.okta.com/docs/guides/refresh-tokens/main/ refresh token response it shows the refresh token format is not in JWT format.
First decide how you want to model this, which might work like this:
User authenticates (and optionally consents)
Create a delegation to represent the user action
Delegation is stored as a database row
Fields include sub, client_id, refresh_token_hash, scopes_issued, claims_issued, issuance time, expiry time
Subsequent token requests are validated against the persisted state
The hash might be the returned to clients, or they may be given a different identifier. It is a pointer to backend state.
You might also need to implement support for refresh token rotation, revocation, auditing of tokens issued and so on. Consider using an authorization server, as described in RFC6749, to handle this stuff for you.
I have been using Flask and JWT to create authentication on my backend. Creating and using access tokens is simple enough, but I've run into some conceptual misunderstanding when trying to discover how to handle the usage and storage of refresh tokens.
Upon initial login, I distribute an access token (with 10 minute expiry) and a refresh token (with 4 day expiry). The 'jti' attribute of the refresh token is stored in a table on the database, along with its expiry date. The access token is stored in memory, and the refresh token is stored in HttpOnly cookies. When the access token expires, a "silent refresh" is sent to the backend with the refresh token. It is first checked for validity (user ID matches up, signed correctly, and is not expired), and then the database is checked to see if it contains that specific refresh token's 'jti'. If it does, then that refresh token is deleted from the database (and can therefore no longer be used) and a new access token and refresh token are sent to the user. This allows for the refresh tokens to only be single use. However, if a user logs out and logs back in repetitively, the refresh token cookie in their browser keeps getting overwritten with a new value (which is fine), but the database now contains a ton of references to "unused" refresh tokens. I'm not sure if my understanding of the JWT workflow is completely incorrect, or if this is normal.
I mainly conceptually followed this guide. Is this repetitive logging in and getting refresh tokens normal? I don't see how to manually find and remove older (but still valid) tokens that are used in the same browser.
Your implementation looks fine. It's normal that you issue new tokens for a new session. I think there are two solutions to your problem:
Add a expiration column to your table with refresh tokens. Then you will be able to remove stale jtis from the table once they're expired.
Instead of keeping information about issued refresh tokens, you can keep information about used refreshed tokens. So, when you issue the token you don't save it in the DB. When the user uses the RT, you can save the jti and expiration in the DB. Whenever a RT is used you check whether the jti is in the DB. If it is, you decline the request. You can remove entries from this table after expiration, as you verify expiration on the RT anyway.
I was worried, as you are, when implementing an Access/Refresh flow with overwritting refresh tokens (there are other strategies,as keeping a blacklist and a whitelist).
I discovered that there were two ways to end with "unused" refresh tokens (as you say) or, as I prefer to name them, "stalled" refresh token (you will see why in a second):
First way: LogOut
As you detected Log Out can lead to stalled refreshed tokens in the database.
Probably, you, as me, (and 90% reading this answer) were just "logging out" from the Client side, aka "deleting Access and Refresh tokens" from the client memory/cookies/localstorage and done. Right? Why so?
However, you can send a "/logout" request to your server with your access token (to authenticate) and your refresh token (in the body), so you can delete the refresh token from the database. I would not pass the JTI, but the whole refresh token (after all it is going to be erased shortly afterwards, so no issues if anyone intercepts it with a MIM attack). This way you can double check the user requesting the /logout is exactly the owner of the refresh token (as a security measure), this security check would be lost if you send just the JTI value (which could lead to an attack: an user requesting a refresh token to be erased, through its JTI, from other user). (Yes you can use the JTI to perform a database check to know its owner, but each time the server performs a database call "God kills a kitten", while you can easily compare the user_id in the access against the user_id in refresh token)
Performing a /logout call, each time the user "/logout" you are really killing her refresh token from the database. And hence the ability to create access tokens if the refresh token got compromised (or sniffed) before the user performed a /logout. If an attacker got the "unused" refresh token, even if the user logged out, could exchange it for a refresh and access token again. Let's reduce the "number of refresh tokens" able to create access tokens for an user.
Second Way: Expired Tokens
A second way to have a "stalled" token is when the client tries to /refresh but the refresh token is already expired. In such case, dont just return an error code that will be used by your app to send the user to the Log In page, but also delete the refresh token from the database. Why do you need to keep it? This cleanup strategy reduces the size of your table and helps to clean your database of already expired refresh tokens. You, ofc, will need a script to clean refresh tokens from users "never-returning" to your app or from users who decided to delete localstorage/cookies, but ey! your cleanup script will be fast as hell now.
This second way is the reason I prefer to call all of them "stalled" because they are sitting there (ones being "unused", others being "expired") and filling your table.
Hope these strategies help your security concerns, a pleasure to meet someone as "geek" as me regarding JWT security.
I'm just learning JWT in nodejs, and I found out about refresh tokens.
As far as I understand, a user gets an access token and a refresh token. After the access token expires, a request containing the refresh token is made to get a new access token. To get a new access token, the server checks if the received refresh token is contained in a database. If the refresh token is stolen, it can easily be deleted from the DB and prevent further refreshes.
My question is: Why don't we just make the access tokens behave like refresh tokens? i.e. We store them in a database and check if they are there when making a request, and when compromised we just delete them?
The key element to answering your question is: You need to add an expiration date on access tokens you deliver to clients. This is the main purpose with refresh token.
Imagine someone steels your access_token, and you didn't make it expirable: It means that as long as you didn't discover that your access_token has been stolen, you're giving literaly a lifetime free pass to whoever has it.
With refresh tokens and expirable access_tokens, you know that the window of vulnerability is really small.
Now your second question: Why don't we make access_tokens behave like refresh_tokens ?
The key idea here is to keep your refresh_token in a safe spot, and only expose access_tokens.
And by the way, refresh_tokens have one job: Carry information to generate new access_tokens, access_tokens on the other hand have their own job: Carry information necessary to give you direct access to resources.
If you pay attention to most serious websites, they have a centralized auth server that serves access_tokens.
Answering comments:
Key difference between them is: refresh token key is like a master key, it stays on the authorization server and is never ever shared with any other server, unlike access token key, it can be passed to another server to authenticate users
in other words:
auth.yourapp.com: stores access_token_key and refresh_token_key
api.yourapp.com: stores access_token_key ONLY, to make sure that users did actualy authenticate on your auth.yourapp.com domain, and api.yourapp.com can easily confirm that. if access_token_key has been compromised, vulnerability has a shorter lifetime, and you can easily isolate the attacked server.
if one of your servers is compromised, the rest is safer.
I'm referencing another SO post that discusses using refresh tokens with JWT.
JWT (JSON Web Token) automatic prolongation of expiration
I have an application with a very common architecture where my clients (web and mobile) talk to a REST API which then talks to a service layer and data layer.
I understand JWT token authentication, but I am a little confused at how I should use refresh tokens.
I want my JWT authentication to have the following properties:
JWT Token has an expiration of 2 hours.
The token is refreshed every hour by the client.
If the user token is not refreshed (user is inactive and the app is not open) and expires, they will need to log in whenever they want to resume.
I see a lot of people claiming to make this a better experience using the concept of a refresh token, however, I don't see the benefit of this. It seems like an added complexity having to manage it.
My questions are the following:
If I WERE to use a refresh token, wouldn't it still be beneficial to have a long term expiration for good practice on that token as well?
If I WERE to use a refresh token, would that token be persisted with the userId and/or JWT token?
When I update my token every 1 hour, how does this work? Will I want to create an endpoint that takes in my JWT token or my refresh token? Will this update the expiration date of my original JWT token, or create a new token?
Is there the need for a refresh token given these details? It seems that If the user is just using a JWT token to grab a new token (per the link above) then the refresh token is obsolete.
Let me come to your questions a little later down the line and start by actually discussing the whole purpose of a refresh token.
So the situation is:
The user opens the app and provides his login credentials. Now, most probably the app is interacting with a REST backend service. REST is stateless, there isn't a way to authorize access to the APIs. Hence, so far in the discussion, there is no way to check if an authorized user is accessing the APIs or is just some random requests coming through.
Now to be able to solve this problem, we need a way to know that the requests are coming from an authorized user. So, what we did was to introduce something called an access token. So now once the user is authenticated successfully, he is issued an access token. This token is supposed to be a long and highly random token (to ensure that it can not be guessed). This is where the JWT comes into the picture. Now you may/may not want to store any user-specific details in a JWT token. Ideally, you would want to just store very simple, extremely non-sensitive details in the JWT. The manipulation of the JWT hash to retrieve other user's details (IDOR etc.) is taken care of by JWT (the library being used) itself.
So, for now, our problem with authorized access is solved.
Now we talk of an attack scenario. Let's say using all of the above user Alice, using the app, has the authorized access token and now her app can make requests to all the APIs and retrieve the data as per her authorization.
Assume that SOMEHOW Alice loses the Access Token or put another way, an adversary, Bob, gets access to Alice's access token. Now Bob, despite being unauthorized, can make requests to all the APIs that Alice was authorized to.
SOMETHING WE IDEALLY DON'T WANT.
Now the solution to this problem is :
Either detect that there is something of this sort happening.
Reduce the attack window itself.
Using just the access token alone, it is hard to achieve condition 1 above, because be it Alice or Bob, it's the same authorized token being used and hence requests form the two users are not distinguishable.
So we try achieving 2 above and hence we add an expiration to the validity of the access token, say the access token is valid for 't' (short-lived) time.
How does it help? Well, even if Bob has the access token, he can use it only while it is valid. As soon as it expires, he will have to retrieve it again. Now, of course, you could say that he can get it the same way he got it the first time. But then again there's nothing like 100% security!
The above approach still has a problem and in some cases an unacceptable one. When the access token expires, it would require the user to enter his login credentials and obtain an authorized access token again, which at least in case of mobile apps, is a bad (not acceptable) user experience.
Solution: This is where the refresh token comes in. It is again a random unpredictable token that is also issued to the app along with the access token in the first place. This refresh token is a very long-lived special token, which makes sure that as soon as the access token expires, it requests the server for a new access token, thus removing the need for the user to re-enter his login credentials to retrieve a new authorized access token, once an existing one has expired.
Now you may ask, Bob can have access to the refresh token as well, similar to the way he compromised the access token. YES. He can. However, now it becomes easy to identify such an incidence, which was not possible in the case of an access token alone, and take the necessary action to reduce the damage done.
How?
For every authenticated user (in case of a mobile app, generally), a one to one mapped refresh token and access token pair is issued to the app. So at any given point in time, for a single authenticated user, there will be only one access token corresponding to a refresh token. Now assume that if Bob has compromised the refresh token, he would be using it to generate an access token (because access token is the only thing which is authorized to access resources through the APIs). As soon as Bob (attacker) requests with the newly generated access token because Alice's (genuine user) access token is still valid, the server would see this as an anomaly, because for a single refresh token there can be only one authorized access token at a time. Identifying the anomaly, the server would destroy the refresh token in question and along with it all, it's associated access tokens will also get invalidated. Thus preventing any further access, genuine or malicious, to any authorization requiring resources.
The user, Alice, would be required to once again authenticate with her credentials and fetch a valid pair of a refresh and access tokens.
Of course, you could still argue that Bob could once again get access to both refresh and access tokens and repeat the entire story above, potentially leading to a DoS on Alice, the actual genuine customer, but then again there is nothing like 100% security.
Also as a good practice, the refresh token should have an expiry, although a pretty long one.
I believe for this scenario you could work with the access token alone, making
life easier for your clients but keeping the security benefits of a refresh token.
This is how it would work:
When your user logs in with credentials (username/password) you return a
short-lived JWT. You also create a db record where you store:
JWT id
user id
IP address
user agent
a valid flag (defaults to TRUE)
createdAt
updatedAt
Your client submits the JWT in every request. As long as the JWT hasn't expired,
it has access to the resources. If the JWT expired, you refresh it
behind the scenes and return both the resource and an additional X-JWT header
with the new JWT.
When the client receives a response with an X-JWT header, it discards the
old JWT and uses the new one for future requests.
How refreshing the JWT works on the server
Look for the matching db record using the JWT id.
Check if the valid flag is still true, otherwise reject.
Optionally, you can compare the request IP address and user agent against
the stored IP address and user agent, and decide to reject if something looks
fishy.
Optionally, you can check the db record's createdAt or updatedAt fields, and
decide not to refresh if too much time has passed.
Update the updatedAt field in the db record.
Return the new JWT (which is basically a copy of the expired JWT, but with an extended expiration time).
This design would also give you the option to revoke all tokens for a user (for
example, if the user loses his phone or updates his password).
Benefits:
Your client never has to check expiration times or make refresh token
requests, all it does is check for an X-JWT header on responses.
You can add custom refresh logic based on IP address, user agent, max-token
age, or a combination of those.
You can revoke some or all tokens for a user.
If I WERE to use a refresh token, wouldn't it still be beneficial to have a long term expiration for good practice on that token as well?
Refresh Tokens are long-lived, Access Tokens are short-lived.
If I WERE to use a refresh token, would that token be persisted with the userId and/or JWT token?
It would be persisted as a separate token on the client, alongside JWT but not inside JWT. UserID/UID can be stored inside the JWT token itself.
When I update my token every 1 hour, how does this work? Will I want to create an endpoint that takes in my JWT token or my refresh token? Will this update the expiration date of my original JWT token, or create a new token?
Yes, you need a separate service that issues and refreshes token. It won't update the expiration of the existing JWT Token. A token is simply JSON field-value pairs that are base64 encoded. So changing the data, changes the output. The token also has the issue date, which will at the very least change on every fresh issue (refresh). So every token will be unique and new. The old tokens will auto-expire, hence you need expiration on all Access Tokens, otherwise they will linger around forever.
The other answer here states that old tokens get destroyed when you issue a new token. That's simply not the case. Tokens cannot be destroyed. In fact, you can harvest hundreds of tokens by constantly contacting the auth server and asking for new fresh tokens using your Refresh Token. Each of those Access Tokens will be valid till their expiry. So expiry is imperative, and it should be short.
Is there really the need for a refresh token given these details? It seems that If the user is just using a JWT token to grab a new token (per the link above) then the refresh token is obsolete.
JWT tokens have client claims. For example is_manager:true claim on a JWT token might allow access to manager-level features. Now if you decide to demote the user from manager to contractor, that won't take effect immediately. The user may still be using the old token. Finally when that expires, he hits the auth server to refresh his token. The auth server issues a new token without the managerial claim and the user won't be able to access managerial features any more. This creates a window during which the user's claims are not in sync with the server. This again explains why Access Tokens should be short-lived so sync'ing can happen often.
Essentially you are updating the authorization checks every 15 minutes, instead of checking them on every single request (which is how typical session-based auth works). If you want real-time permissions instead of every-15-minute refreshes, then JWT may not be a good fit.
i have to confess i've had this question for a very long time, never really understand.
say auth token is like a key to a safe, when it expires it's not usable anymore. now we're given a magic refresh token, which can be used to get another usable key, and another... until the magic key expires. so why not just set the expiration of the auth token as the same as refresh token? why bother at all?
what's the valid reason for it, maybe a historical one? really want to know. thanks
I was reading an article the other day by Taiseer Joudeh and I find it very useful he said:
In my own opinion there are three main benefits to use refresh tokens which they are:
Updating access token content: as you know the access tokens are self contained tokens, they contain all the claims (Information) about the authenticated user once they are generated, now if we issue a long lived token (1 month for example) for a user named “Alex” and enrolled him in role “Users” then this information get contained on the token which the Authorization server generated. If you decided later on (2 days after he obtained the token) to add him to the “Admin” role then there is no way to update this information contained in the token generated, you need to ask him to re-authenticate him self again so the Authorization server add this information to this newly generated access token, and this not feasible on most of the cases. You might not be able to reach users who obtained long lived access tokens. So to overcome this issue we need to issue short lived access tokens (30 minutes for example) and use the refresh token to obtain new access token, once you obtain the new access token, the Authorization Server will be able to add new claim for user “Alex” which assigns him to “Admin” role once the new access token being generated
Revoking access from authenticated users: Once the user obtains long lived access token he’ll be able to access the server resources as long as his access token is not expired, there is no standard way to revoke access tokens unless the Authorization Server implements custom logic which forces you to store generated access token in database and do database checks with each request. But with refresh tokens, a system admin can revoke access by simply deleting the refresh token identifier from the database so once the system requests new access token using the deleted refresh token, the Authorization Server will reject this request because the refresh token is no longer available (we’ll come into this with more details).
No need to store or ask for username and password: Using refresh tokens allows you to ask the user for his username and password only one time once he authenticates for the first time, then Authorization Server can issue very long lived refresh token (1 year for example) and the user will stay logged in all this period unless system admin tries to revoke the refresh token. You can think of this as a way to do offline access to server resources, this can be useful if you are building an API which will be consumed by front end application where it is not feasible to keep asking for username/password frequently.
I would like to add to this another perspective.
Stateless authentication without hitting the DB on each request
Let's suppose you want to create a stateless (no session) security mechanism that can do authentication of millions of users, without having to make a database call to do the authentication. With all the traffic your app is getting, saving a DB call on each request is worth a lot! And it needs to be stateless so it can be easily clustered and scaled up to hundreds or even thousands of servers.
With old-fashioned sessions, the user logs in, at which point we read their user info from the database. To avoid having to read it again and again we store it in a session (usually in memory or some clustered cache). We send the session ID to the client in a cookie, which is attached to all subsequent requests. On subsequent requests, we use the session ID to lookup the session, that in turn contains the user info.
Put the user info directly in the access token
But we don't want sessions. So instead of storing the user info in the session, let's just put it in an access token. We sign the token so no one can tamper with it and presto. We can authenticate requests without a session and without having to look up the user info from the DB for each request.
No session ... no way to ban users?
But not having a session has a big downside. What if this user is banned for example? In the old scenario we just remove his session. He then has to log in again, which he won't be able to do. Ban completed. But in the new scenario there is no session. So how can we ban him? We would have to ask him (very politely) to remove his access token. Check each incoming request against a ban list? Yes, would work, but now we again have to make that DB call we don't want.
Compromise with short-lived tokens
If we think it's acceptable that a user might still be able to use his account for, say, 10 minutes after being banned, we can create a situation that is a compromise between checking the DB every request and only on login. And that's where refresh tokens come in. They allow us to use a stateless mechanism with short-lived access tokens. We can't revoke these tokens as no database check is done for them. We only check their expiry date against the current time. But once they expire, the user will need to provide the refresh token to get a new access token. At this point we do check the DB and see that the user has been banned. So we deny the request for an access token and the ban takes effect.
The referenced answer (via #Anders) is helpful, It states:
In case of compromise, the time window it's valid for is limited, but
the tokens are used over SSL, so unlikely to be compromised.
I think the important part is that access tokens will often get logged (especially when used as a query parameter, which is helpful for JSONP), so it's best for them to be short-lived.
There are a few additional reasons, with large-scale implementations of OAuth 2.0 by service providers:
API servers can securely validate access tokens without DB lookups or RPC calls if it's okay to not worry about revocation. This can have strong performance benefits and lessen complexity for the API servers. Best if you're okay with a token revocation taking 30m-60m (or whatever the length of the access token is). Of course, the API servers could also keep an in-memory list of tokens revoked in the last hour too.
Since tokens can have multiple scopes with access to multiple different API services, having short-lived access tokens prevents a developer of API service for getting a lifelong access to a user's data on API service B. Compartmentalization is good for security.
Shortes possible answer:
Refresh tokens allow for scoped / different decay times of tokens. Actual resource tokens are short lived, while the refresh token can remain valid for years (mobile apps). This comes with better security (resource tokens don't have to be protected) and performance (only the refresh token API has to check validity against DB).
The following is an addition to the benefits of refresh tokens that are already mentioned.
Safety First!
Access tokens are short-lived. If someone steals an access token, he will have access to resources only until access token expires.
"...But what if a refresh token is stolen?"
If an attacker steals the refresh token, he can obtain an access token. For this reason, it it recommended that a new refresh token is issued each time a new access token is obtained. If the same refresh token is used twice, it probably means that the refresh token has been stolen.
When the refresh token changes after each use, if the authorization
server ever detects a refresh token was used twice, it means it has
likely been copied and is being used by an attacker, and the
authorization server can revoke all access tokens and refresh tokens
associated with it immediately.
https://www.oauth.com/oauth2-servers/making-authenticated-requests/refreshing-an-access-token/
Of course, this is just another layer of security. The attacker can still have time to obtain access tokens, until the refresh token is used a second time (either by the attacker or the real user).
Always keep in mind that the refresh token must be stored as securely as possible.