What are the possible reasons that can cause token to become expired (besides having the user un-authorising the app)?
My problem is that I have an app with several thousands of users, all API communication works perfectly but for some users I am getting the invalid or expired token error, my initial though was that they are users who canceled the authentication to the app but I've contacted some of them and they haven't revoked the access.
Any ideas what other issues can cause that error?
Check the integrity of an access token at any time by calling the GET account/verify_credentials while using that access token.
Its mentioned and by research I came to know that:
Your access token will be invalid if a user explicitly rejects your
application from their settings or if a Twitter admin suspends your
application. If your application is suspended there will be a note on
your application page saying that it has been suspended.
Why is my twitter oauth access token invalid / expired ?
Check this post: invalid / expired access tokens.
There is one post in google groups that says:
You don't get a second chance, and this is by design. OAuth requests
have a unique signature; once a particular request is submitted, it
can't be submitted again.
If they enter the pin correctly, all is well, you get an access token.
If they enter the pin wrong, you get 401 Unauthorized - which is
expected.
But if they then try again to enter the pin, even the correct pin
shows as unauthorized.
Check this link for the above reference.
Some suggestions by twitter employee for the same problem:
I guess there are two things I would suggest at this point: 1.) Go to
your application settings and use the "Reset keys" tab to reset your
consumer key and secret, then update those values in the app and
verify that you still see the same behavior. 2.) Try passing
oauth_callback in your request_token call. Honestly I don't think this
will make a difference, but I want to try and be as rigorous as I can
here.
Also check this discussion saying:
You need to use the oauth_token and oauth_token_secret returned from
the oauth/access_token call instead of the one in your app's settings
in dev.twitter.com
I was getting same error then I changed (access_token) to (access_token_key) and it worked for me.
I hope it will help someone.
In addition to the comments everyone else has made, sometimes the twitter api will return a "invalid token" error when the token isn't the problem. I've noticed it the most when I've built a request string that doesn't parse correctly. For example, once I was getting that error when I was passing in screen_name's that had symbols that weren't URI-encodable. I also have gotten it when I passed in empty values like this (where the cursor is empty):
https://api.twitter.com/1/followers.json?cursor=&screen_name=whatevah
Could you give us the specifics of the calls that are returning this error?
Have you confirmed that the tokens worked at one time? In an OAuth system I worked on, there was an error in how tokens were securely stored and retrieved that caused a small percentage of them to become corrupted. If you can confirm that the tokens worked in the past, that's a good first step.
When you retrieve the tokens from storage, are they unchanged? Is it possible for them to get corrupted with the way you're managing them?
Put some logging in place to keep track of when tokens work and fail. Does a token ever start working again after it has failed once? If you fail to use a token for 30 days, does it expire? With a detailed log, you can start identifying the expired tokens and look for patterns in use to point to what might cause them to expire.
Be sure to explore other possibilities as well. How do users revoke tokens in Twitter? Is it easy to accidentally do that? For users with failed tokens, do they have other authorized apps that have stopped working as well?
First of all nice question Ran.
I want to ask you that have you gone through Twitter developers??
Sometimes it becomes ambiguous that which token to use since Twitter provides two pairs of tokens and the library.One of them is a secret key.
You need to select those token which starts with your Twitter ID followed by a hyphen.
Now your question is this error happens with some of yours users. So here is the answer that an app itself finds ambiguous to choose the token.
Though I might not be completely right, but I recommend you to try this solution at least once.
It might be possible these users have not revoked access. But in my experience an access token can also get expired after the user (in test cases: me) changed his/her password.
When the user does that, you can no longer use the REST API of stream API on that user's scope. Please adapt your application to handle with that situation. Revoke the user's session, so when he comes back to your application, he/she can be redirected to Twitter again to start a new OAuth access token process. Or send him/her an e-mail to kindly ask to reconnect. Vimeo/Windows/... are some of the people handling expired tokens with e-mails.
Have fun!
My God's answer is correct but I will share my answer from another question explaining how it could be your computer's clock:
If your OAuth flow was working one day and failing the next, check your computer's clock. I was running a Vagrant box that somehow had its time set to the day before, which caused the Twitter API to return {"code":89,"message":"Invalid or expired token."}. This may also appear as 401 timestamp out of bounds. You can use this command to update your clock in Ubuntu:
sudo ntpdate time.nist.gov
Alternative method if ntpdate isn't available on your system:
sudo date -s "$(wget -qSO- --max-redirect=0 google.com 2>&1 | grep Date: | cut -d' ' -f5-8)Z"
if your Access Token=738629462149844993-FcWHjfcucCLGEosyGGQ38qI******iC then don't forget to mention hyphen (-) followed by your USERID.
May be this will be helpful for you.I faced the same problem.
Please find the below piece of code snippet
$code = $tmhOAuth->user_request(array(
'method' => 'POST',
'url' => $tmhOAuth->url('oauth/access_token', ''),
'params' => array(
'oauth_verifier' => trim($params['oauth_verifier']),
)
));
if ($code == 200) {
$oauth_creds = $tmhOAuth->extract_params($tmhOAuth->response['response']);
// echo '<pre>';print_r($oauth_creds);exit;
$tmhOAuth->reconfigure(array_merge($tmhOAuth->config, array(
'token' => $oauth_creds['oauth_token'],
'secret' => $oauth_creds['oauth_token_secret'],
)));
$code = $tmhOAuth->user_request(array(
'url' => $tmhOAuth->url('1.1/account/verify_credentials')
));
}
The error invalid or expired token can be linked with the fact that one is not paying.
Without paying one will only be able to create the dev environment (sandbox).
As I have answered here:
Counts is only available to paid premium accounts, and one needs to pay for premium access.
Use this link to Apply for access.
Try to regenerate the keys again and save them properly.
For me, it happened because after regenerating one of the keys I did not update other keys. Therefore removed and regenerated all 4 keys again (CONSUMER_KEY, CONSUMER_SECRET, ACCESS_KEY, ACCESS_SECRET). And tried to execute it again and it worked this time.
Related
We keep playing this cat and mouse game with Robinhood.com. I have a trading app which used to trade stocks with Robinhood, but they keep changing the unsupported unofficial API to make it difficult for traders to use. I know that many people are doing the same thing and I want to reach out to them to see if there is a new answer. The latest problem is when I try to get a Bearer token using the URL https://api.robinhood.com/oauth2/token/ the API returns the following JSON: {"detail":"This version of Robinhood is no longer supported. Please update your app or use Robinhood for Web to log in to your account."}. This started happening on 4/26/2019.
Has anyone found a work around for this, yet, or have they finally beaten us into submission?
A more complete solution (not need browser):
Use requests.session.
Obtain the login page by making a GET request to "https://robinhood.com/login".
At this point the session's cookies will contain 'device_id'.
Obtain this device_id and use it in making the oauth2 token request to "https://api.robinhood.com/oauth2/token/" also add in the data request "challenge_type" (either "sms" or "email").
This request will fail with a 400 error code. Robinhood will send an SMS message or Email with a temporary (5 minute) code.
Also at this point use the 400 response's body to get "id" from "challenge" inside of the JSON object.
Confirm the challenge by making a POST request to "https://api.robinhood.com/challenge/CHALLENGEID/respond/" where CHALLENGEID is the same id mentioned in the first failed /oauth2/token/ POST request.
Make the same POST request to "https://api.robinhood.com/oauth2/token/" and include in the header "X-ROBINHOOD-CHALLENGE-RESPONSE-ID" with the value CHALLENGEID.
You can reuse a device_id with user/pass after this even after logging out.
Be cautious with storing device_id as it is the result of user/pass login and successful SMS/email 2FA.
Just got it working. At the risk of them seeing this post and changing it more, here we go:
First, you're going to want to log into your RH account in a web browser
View Source on the page, and look for clientId - it should be a big hex number separated by dashes
Add that number to your POST requests to /oauth2/token under the field device_token
There's probably another way to retrieve the device token, and I'm not even sure it's unique, but that way should work.
Good to be back here after a very long time.
Not sure if anyone is still looking for answers to this, but I have a very simple solution.
At Robinhood's login screen, enter your username/email and your password, press F12 on your keyboard to bring up the console panel and switch to the "Network" tab then wait for the page to load completely. (During this time you will see a list of items being loaded rapidly depending on the connection speed.)
At this time you can keep clearing the list by clicking on the button highlighted in the below image.
Click on button highlighted repeatedly until the list is empty
Now, log into your Robinhood account. At this point your console should display a list similar to the one shown below.
Look for the name "token/", most likely it will be the second one you get all the information you need. And this information will be under the Headers then Request Payload
I was able to find this with past knowledge and experience of web scraping for fun. And also, I needed to know this as well, since I recently started doing trades via Robinhood.
Hope this help you curious ones out there.
For my Robinhood account I am using Google Authenticator for my 2FA. What I have so far is that I send the original call that I was sending before to https://api.robinhood.com/oauth2/token/. This is giving me a response of:
{"mfa_required":true,"mfa_type":"app"}
I then repeat my oauth token request, but this time providing the value from Google Authenticator (so my GUI has to prompt me to fill it in) with this payload in the request to https://api.robinhood.com/oauth2/token/:
{"grant_type":"password","scope":"internal","client_id":"c82SH0WZOsabOXGP2sxqcj34FxkvfnWRZBKlBjFS","expires_in":86400,"device_token":"***","username":"***","password":"****","mfa_code":"***"}
and then I am getting an access token in reply
I know this is not the first time the topic is treated in StackOverflow, however, I have some questions I couldn't find an answer to or other questions have opposed answers.
I am doing a rather simple REST API (Silex-PHP) to be consumed initially by just one SPA (backbone app). I don't want to comment all the several authentication methods in this question as that topic is already fully covered on SO. I'll basically create a token for each user, and this token will be attached in every request that requires authentication by the SPA. All the SPA-Server transactions will run under HTTPS. For now, my decision is that the token doesn't expire. Tokens that expire/tokens per session are not complying with the statelessness of REST, right? I understand there's a lot of room for security improvement but that's my scope for now.
I have a model for Tokens, and thus a table in the database for tokens with a FK to user_id. By this I mean the token is not part of my user model.
REGISTER
I have a POST /users (requires no authentication) that creates a user in the database and returns the new user. This complies with the one request one resource rule. However, this brings me certain doubts:
My idea is that at the time to create a new user, create a new token for the user, to immediately return it with the Response, and thus, improving the UX. The user will immediately be able to start using the web app. However, returning the token for such response would break the rule of returning just the resource. Should I instead make two requests together? One to create the user and one to retrieve the token without the user needing to reenter credentials?
If I decided to return the token together with the user, then I believe POST /users would be confusing for the API consumer, and then something like POST /auth/register appears. Once more, I dislike this idea because involves a verb. I really like the simplicity offered in this answer. But then again, I'd need to do two requests together, a POST /users and a POST /tokens. How wrong is it to do two requests together and also, how would I exactly send the relevant information for the token to be attached to a certain user if both requests are sent together?
For now my flow works like follows:
1. Register form makes a POST /users request
2. Server creates a new user and a new token, returns both in the response (break REST rule)
3. Client now attaches token to every Request that needs Authorization
The token never expires, preserving REST statelessness.
EMAIL VALIDATION
Most of the current webapps require email validation without breaking the UX for the users, i.e the users can immediately use the webapp after registering. On the other side, if I return the token with the register request as suggested above, users will immediately have access to every resource without validating emails.
Normally I'd go for the following workflow:
1. Register form sends POST /users request.
2. Server creates a new user with validated_email set to false and stores an email_validation_token. Additionally, the server sends an email generating an URL that contains the email_validation_token.
3. The user clicks on the URL that makes a request: For example POST /users/email_validation/{email_validation_token}
4. Server validates email, sets validated_email to true, generates a token and returns it in the response, redirecting the user to his home page at the same time.
This looks overcomplicated and totally ruins the UX. How'd you go about it?
LOGIN
This is quite simple, for now I am doing it this way so please correct me if wrong:
1. User fills a log in form which makes a request to POST /login sending Basic Auth credentials.
2. Server checks Basic Auth credentials and returns token for the given user.
3. Web app attached the given token to every future request.
login is a verb and thus breaks a REST rule, everyone seems to agree on doing it this way though.
LOGOUT
Why does everyone seem to need a /auth/logout endpoint? From my point of view clicking on "logout" in the web app should basically remove the token from the application and not send it in further requests. The server plays no role in this.
As it is possible that the token is kept in localStorage to prevent losing the token on a possible page refresh, logout would also imply removing the token from the localStorage. But still, this doesn't affect the server. I understand people who need to have a POST /logout are basically working with session tokens, which again break the statelessness of REST.
REMEMBER ME
I understand the remember me basically refers to saving the returned token to the localStorage or not in my case. Is this right?
If you'd recommend any further reading on this topic I'd very much appreciate it. Thanks!
REGISTER
Tokens that expire/tokens per session are not complying with the statelessness of REST, right?
No, there's nothing wrong with that. Many HTTP authentication schemes do have expiring tokens. OAuth2 is super popular for REST services, and many OAuth2 implementations force the client to refresh the access token from time to time.
My idea is that at the time to create a new user, create a new token for the user, to immediately return it with the Response, and thus, improving the UX. The user will immediately be able to start using the web app. However, returning the token for such response would break the rule of returning just the resource. Should I instead make two requests together? One to create the user and one to retrieve the token without the user needing to reenter credentials?
Typically, if you create a new resource following REST best practices, you don't return something in response to a POST like this. Doing this would make the call more RPC-like, so I would agree with you here... it's not perfectly RESTful. I'll offer two solutions to this:
Ignore this, break the best practices. Maybe it's for the best in this case, and making exceptions if they make a lot more sense is sometimes the best thing to do (after careful consideration).
If you want be more RESTful, I'll offer an alternative.
Lets assume you want to use OAuth2 (not a bad idea!). The OAuth2 API is not really RESTful for a number of reasons. I'm my mind it is still better to use a well-defined authentication API, over rolling your own for the sake of being RESTful.
That still leaves you with the problem of creating a user on your API, and in response to this (POST) call, returning a secret which can be used as an access/refresh token.
My alternative is as follows:
You don't need to have a user in order to start a session.
What you can do instead is start the session before you create the user. This guarantees that for any future call, you know you are talking to the same client.
If you start your OAuth2 process and receive your access/refresh token, you can simply do an authenticated POST request on /users. What this means is that your system needs to be aware of 2 types of authenticated users:
Users that logged in with a username/password (`grant_type = passsword1).
Users that logged in 'anonymously' and intend to create a user after the fact. (grant_type = client_credentials).
Once the user is created, you can assign your previously anonymous session with the newly created user entity, thus you don't need to do any access/refresh token exchanges after creation.
EMAIL VALIDATION
Both your suggestions to either:
Prevent the user from using the application until email validation is completed.
Allow the user to use the application immediately
Are done by applications. Which one is more appropriate really depends on your application and what's best for you. Is there any risk associated with a user starting to use an account with an email they don't own? If no, then maybe it's fine to allow the user in right away.
Here's an example where you don't want to do this: Say if the email address is used by other members of your system to add a user as a friend, the email address is a type of identity. If you don't force users to validate their emails, it means I can act on behalf of someone with a different email address. This is similar to being able to receive invitations, etc. Is this an attack vector? Then you might want to consider blocking the user from using the application until the email is validated.
You might also consider only blocking certain features in your application for which the email address might be sensitive. In the previous example, you could prevent people from seeing invitations from other users until the email is validated.
There's no right answer here, it just depends on how you intend to use the email address.
LOGIN
Please just use OAuth2. The flow you describe is already fairly close to how OAuth2 works. Take it one step further an actually use OAuth2. It's pretty great and once you get over the initial hurdle of understanding the protocol, you'll find that it's easier than you thought and fairly straightforward to just implement the bits you specifically need for your API.
Most of the PHP OAuth2 server implementations are not great. They do too much and are somewhat hard to integrate with. Rolling your own is not that hard and you're already fairly close to building something similar.
LOGOUT
The two reasons you might want a logout endpoint are:
If you use cookie/session based authentication and want to tell the server to forget the session. It sounds like this is not an issue for you.
If you want to tell the server to expire the access/refresh token earlier. Yes, you can just remove them from localstorage, and that might be good enough. Forcing to expire them server-side might give you that little extra confidence. What if someone was able to MITM your browser and now has access to your tokens? I might want to quickly logout and expire all existing tokens. It's an edge case, and I personally have never done this, but that could be a reason why you would want it.
REMEMBER ME
Yea, implementing "remember me" with local storage sounds like a good idea.
I originally took the /LOGON and /LOGOUT approach. I'm starting to explore /PRESENCE. It seems it would help me combine both knowing someone's status and authentication.
0 = Offline
1 = Available
2 = Busy
Going from Offline to anything else should include initial validation (aka require username/password). You could use PATCH or PUT for this (depending how you see it).
You are right, SESSION is not allowed in REST, hence there is no need to login or logout in REST service and /login, /logout are not nouns.
For authentication you could use
Basic authentication over SSL
Digest authentication
OAuth 2
HMAC, etc.
I prefer to use PUBLIC KEY and PRIVATE KEY [HMAC]
Private key will never be transmitted over web and I don't care about public key. The public key will be used to make the user specific actions [Who is holding the api key]
Private key will be know by client app and the server. The private key will be used to create signature. You generate a signature token using private key and add the key into the header. The server will also generate the signature and validate the request for handshake.
Authorization: Token 9944b09199c62bcf9418ad846dd0e4bbdfc6ee4b
Now how you will get private key? you have to do it manually like you put facebook, twitter or google api key on you app.
However, in some case you can also return [not recommended] the key only for once like Amazon S3 does. They provide "AWS secret access key" at the registration response.
So I am updating an older desktop app (written in VB, .net 4.0) with facebook integration and followed the guide found here, and have been able to successfully get a token (by parsing the uri of the embedded webview if it contains "token="). Now my problem is if I try to login with a facebook account that has already approved the app in a prior session, the webview just gets redirected to https://www.facebook.com/connect/login_success.html without any token information.
Do I HAVE to log all of the tokens I generate manually (ie on successful token generation, I can call their profile info, use their FB ID as key and save the token)? Even if I do, since the email and password is input directly into the facebook login window, how do I check if the user already has a token?
Thanks in advance
The access token can change any time, you need to get it everytime. After getting the token, I immediately get the user information https://graph.facebook.com/me?access_token=??? and use that ID to find their database information.
I couldn't quickly find facebook information but on google's oauth information it says "The access token is also associated with a limited scope that define the kind of data the your client application has access to (for example "Manage your tasks"). An important goal for OAuth 2.0 is to provide secure and convenient access to the protected data, while minimizing the potential impact if an access token is stolen."
https://code.google.com/p/google-api-php-client/wiki/OAuth2
Ok so I finally figured it out myself. My mistake was apparently requesting the access_token directly (ie https://www.facebook.com/dialog/oauth?response_type=token...) to try and save time.
I fixed it by making a request for a 'code' instead (ie https://www.facebook.com/dialog/oauth?response_type=code), which I then use to make a second request to retrieve an access token as documented here: https://developers.facebook.com/docs/facebook-login/login-flow-for-web-no-jssdk/, "Exchanging code for an access token" section a bit lower on the page.
Hope this helps someone in the future, this was very frustrating on my part.
Regards,
Prince
I am attempting to create a login system for my website that permits both authentication via Google's API and access to any of the OAuth-supported Google Data APIs while ideally only showing the user one prompt ever, no matter if he's creating an account or logging into his existing one. I want to minimize the number of times he's asked for approval.
I am aware that Google provides Hybrid OpenID/OAuth for this purpose, but the issue is that every time I add OAuth extensions to my OpenID request, it never remembers the user's approval for that request. Is there any way for the approval to be remembered when I am doing Hybrid OpenID/OAuth? If I just do OpenID without OAuth extensions, everything is remembered just fine and it doesn't keep bugging the user with the prompt.
Here are the pertinent extensions I'm sending in addition to my OpenID request, which result in me getting an OAuth request token (good) but cause the approval to never get remembered (bad).
PHP syntax:
$args["openid.ns.ext2"] = 'http://specs.openid.net/extensions/oauth/1.0';
$args["openid.ext2.consumer"] = 'www.MYSITE.com';
$args["openid.ext2.scope"] = 'http://www-opensocial.googleusercontent.com/api/people/';
$args["openid.mode"] = 'checkid_setup';
$args["openid.realm"] = 'http://www.MYSITE.com/';
Is it normal for Hybrid OpenID/OAuth to act this way (not remembering the last OAuth authorization)? What is the best way to get around this? I have thought of storing cookies on the user's computer to link to somewhere in my database so I could use the last access token again, etc... (the issue here being I don't know whose token to look up unless I know who the user is...a circular problem). And doing an OpenID-only request to get his user ID to see if he has an account in order to look up his access token, followed by an OpenID+OAuth request (if an access token for him isn't stored) would result in two prompts, which really wouldn't help.
It also seems like Hybrid only supports OAuth 1.0, which I think is fine until 2015, so it's not an issue right now for me. I am assuming they will support OAuth 2.0 in the future.
Is checkid_immediate relevant to this in any way? I'm just not sure how to use this to accomplish what I want.
I would suggest using OAuth 2.0. This supports getting both identity and access to APIs -- so accomplishes the same end goal, but is much easier than OAuth 1 Hybrid.
Take a look here:
https://developers.google.com/accounts/docs/OAuth2Login
The scopes you're trying to access are included in the URL (see "Forming the URL"). The referenced doc lists the scopes required for getting identity/profile information. You can simply add additional scopes to the string, comma-delimited in order to request access to other APIs. The resulting access token will access both the APIs and identity information (via the UserInfo API endpoint mentioned).
That said, what you're trying to do with OpenID 2.0/OAuth 1 hybrid should work-- and the user should see a checkbox for "remembering" the authorization. If you really want to debug this further, it'd be helpful to have a webpage you can point to which kicks off this authentication+authorization flow so we can see what's happening.
I figured out that checkid_immediate (and x-has-session, not sure if that's needed or even working) is allowing me to determine whether or not a user is logged in without prompting him, and if he is, it is giving me a claimed_id by which I can identify the user. That's exactly what I needed. The original question is solved, but I do want to figure out how to use identify with OAuth 2.0 because I have already implemented that.
Furthermore, I've noticed that when using OpenID/OAuth that the user still gets asked to authorize OAuth even after he's authorized OpenID. I can't see the advantage to the hybrid approach from the user's perspective.
If the user is logged out of Google, that's a total of three prompts just to sign up for my website and grab his name and profile image.
If anyone wondered, here are the steps necessary to get Hybrid OpenID/OAuth completely working (an overview). I was confused thoroughly throughout this process, so I hope this helps someone.
Do normal OpenID handshake and add on AX extensions for OAuth 1.0.
Use 'checkid_immediate' to permit probing for an active Google session without prompting the user. Use *claimed_id* as a unique identifier to link the user to your database.
If 'setup_needed' is returned, use 'checkid_setup' so the user is prompted and verified before continuing.
This leaves you with two possibilities. *checkid_immediate* returning immediately giving you a claimed_id, or a claimed_id coming through after *checkid_setup* (basically sign-up) succeeds.
Hybrid OpenID/OAuth 1.0 will give you an authorized request token.
Use the authorized request token to get an access token (you only need to call OAuthGetAccessToken)
Use that OAuth 1.0 access token to do whatever you want.
I was successful in using OAuthGetAccessToken to get an access token from the authorized request token my Hybrid OAuth dance, omitting the 'oauth_verifier' parameter (irrelevant to Hybrid).
I was successful in using OAuthGetAccessToken to get an access token after my Hybrid OAuth dance, omitting the 'oauth_verifier' parameter (irrelevant to Hybrid).
In a PHP/Zend environment:
$config = array(
'accessTokenUrl' => 'https://www.google.com/accounts/OAuthGetAccessToken',
'consumerKey' => $consumer_key,
'consumerSecret' => $consumer_secret
);
$consumer = new Zend_Oauth_Consumer($config);
$zendRToken = new Zend_Oauth_Token_Request(); // create class from request token we already have
$zendRToken->setToken($requestToken);
try{
$accessToken = $consumer->getAccessToken(array(
'oauth_token' => $requestToken,
// 'oauth_verifier' => '', // unneeded for Hybrid
'oauth_timestamp' => time(),
'oauth_nonce' => md5(microtime() . mt_rand()),
'oauth_version' => '1.0'
), $zendRToken);
} catch (Zend_Oauth_Exception $e){
echo $e->getMessage() . PHP_EOL;
exit;
}
echo "OAuth Token: {$accessToken->getToken()}" . PHP_EOL;
echo "OAuth Secret: {$accessToken->getTokenSecret()}" . PHP_EOL;
I have to build an App that need authentication over a DB (online).
When application load, at first appear a login screen to insert user credentials.
Thus after a correct login, user can access every areas of this app.
I think to use this steps, what do you think about?
1) Build a PHP (or other lang) Webservice that accept username/password(crypt) and check this data. When user is found, create a token with some strange unique string and adding a expiration time information. Send token back as response with some sort of json structure.
2) The IOS APP call this service passing username/password, if the webservice response is positive, store the received token in NSUserdefault and add time of creation (so i can calculate when it expire.
3) From my APP i can make request toward webservice sending my token. WS checks Token validity and send back a response.
Is this a good practice ???
Yes and no.
I think your approach will work as you wrote it. But keep in mind, that your users needs an internet connection to use your app. So I would design the structure in a way it has also a use for the user, if he has no internet connection.
I also don't know how good your expirience is with Webservices and the communication with them. If you send the data, you should also encrypt the sent data, because they are the credentials of the user. So it's not save to send them as GET Values for examples in a PHP script...
I hope my answer did help a little bit. If you have specific questions on this type of webservice, just ask. I did this a few times before. ;-)
Sandro Meier