I've been asked by my employer to implement a log-in system for our web application using users' GitHub accounts. I've looked around online but I haven't been able to find a clear explanation of how to go about doing this with GitHub accounts (as opposed to with Facebook or Google accounts).
I just spent about a week's worth of effort figuring out how to do this, so I thought I'd write up an explanation to save future developers time.
The short(er) answer
You'll want to follow this guide in GitHub's docs ("Authorizing OAuth Apps"), with some additions (explained below) to allow it to work as a method of user authentication.
I implemented the "web application flow" for when our application will be deployed on our company's servers (where we can keep our company's GitHub app's "client secret" a secret), and the "device flow" for when our application will be deployed on our client's computers (because in that situation we won't be able to keep our "client secret" a secret).
GitHub's guide doesn't mention the steps below (because that guide is not intended specifically for implementing social login), but to get social login working I also did the following:
I created a users database table, with the idea being that each GitHub account used to log in would have its own corresponding row in this table.
Example users table schema:
id - INTEGER
email - VARCHAR
name - VARCHAR
github_id - VARCHAR
I created an oauth_tokens database table to store a copy of all of the GitHub access tokens that our back-end receives from GitHub.
This is needed to prevent other malicious websites from impersonating our users with valid GitHub access tokens generated by the user authorizing an access token for the malicious website.
Example oauth_tokens table schema:
id - INTEGER
user_id - INTEGER
access_token - VARCHAR
expires_at - DATETIME
refresh_token - VARCHAR
refresh_token_expires_at - DATETIME
device_code - VARCHAR <-- Used for the "device flow". I have the back-end send the
front-end the device code immediately upon starting the device flow, and I then
have the front-end poll the back-end with it until the back-end has received
the access token from GitHub, at which point the front-end discards the device
code and uses the access token as its authentication token.
I had the back-end send the front-end (the user) the GitHub access token for it to present with future requests as its authentication mechanism.
The front-end should store the token in localStorage if you want the user to remain logged in even after they close the browser tab they logged in with.
I added middleware on the back-end that--for each incoming request--looks up the provided access token in our database to see if it's expired, and if so, attempts to refresh it. If it succeeds in refreshing the token, it proceeds with the request as normal and includes the new access token in the response to the front-end in a custom response header the front-end is keeping an eye out for (I named it x-updated-access-token). If it fails to refresh the token, it aborts the request and sends a 401 response that the front-end takes as a signal to redirect the user to the login page.
Setting up your app to only allow unexpired access tokens to serve as a method of authentication is necessary to make it possible for the user to sign out of the application remotely from their settings page at GitHub.com.
I added front-end code to handle the saving / updating / removing of the GitHub access token, both to/from localStorage as well as to all requests to the back-end, as well as redirecting to a /login route if the front-end doesn't find an "access_token" localStorage variable set.
The code is further below if you want an in-depth explanation, but basically I used this article as a rough guide for how the front-end code should work for the "web application flow": OpenID Connect Client by Example - Codeburst.io
More information
To clarify some vocabulary: The goal here is to do user authentication via social login. Social login is a type of single-sign on.
The first thing you should understand is that--as of the time I'm writing this--GitHub has not set itself up to be a provider of social login in the way Facebook and Google have.
Facebook and Google both have developed special JavaScript libraries that you can use to implement social login without needing to write any(?) login-specific back-end code. GitHub has no such library, and from what I can tell it's not even possible for a third party to develop such a library because GitHub's API doesn't offer the functionality required to make such a library possible (specifically, they seem to support neither the "implicit flow" nor OpenID Connect).
The next thing you should understand is that--as of the time I'm writing this--GitHub's API does not seem to support the use of OpenID Connect to implement social login using GitHub accounts.
When I started doing research into how to implement social login I was confused by the fact that the most-recent online guides were saying that OpenID Connect was the current best-practice way to do it. And this is true, if the Identity Provider (e.g. GitHub) you're using supports it (i.e. their API can return OpenID Connect ID tokens). As far as I can tell, GitHub's API doesn't currently have the ability to return OpenID Connect ID tokens from the endpoints we'd need to request them from, although it does seem they support the use of OpenID Connect tokens elsewhere in their API.
Thus, the way web apps will generally want to implement social login with GitHub accounts is to use the OAuth 2.0 flow that most websites used before OpenID Connect, which most online resources call the "authorization code flow", but which GitHub's docs refer to as the "web application flow". It's just as secure but requires some more work/code than the other methods to implement properly. The takeaway is that implementing social login with GitHub is going to take more time than using an Identity Provider like Facebook or Google that have streamlined the process for developers.
If you (or your boss) still want to use GitHub for social login even after understanding it's going to take more time, it's worth spending some time to watch some explanations of how the OAuth 2.0 flow works, why OpenID Connect was developed (even though GitHub doesn't seem to support it), and become familiar with some key technical terms, as it'll make it easier to understand the GitHub guide.
OAuth 2.0
The best explanation of OAuth 2.0 that I found was this one by Okta: An Illustrated Guide to OAuth and OpenID Connect
The most important technical terms:
Identity Provider - This is GitHub, Facebook, Google, etc.
Client - This is your app; specifically, the back-end part of your app.
Authorization Code - "A short-lived temporary code the Client gives the [Identity Provider] in exchange for an Access Token."
Access Token: This is what lets your app ask GitHub for information about the user.
You may also find this graph helpful:
The slide title is "OIDC Authorization Code Flow" but the same flow is used for a non-OIDC OAuth 2.0 authorization code flow, with the only difference being that step 10 doesn't return an ID token, just the access token and refresh token.
The fact that step 11 is highlighted in green isn't significant; it's just the step the presenter wanted to highlight for this particular slide.
The graph shows the "Identity Provider" and "Resource Server" as separate entities, which might be confusing. In our case they're both GitHub's API; the "Identity Provider" is the part of GitHub's API that gets us an access token, and the "Resource Server" is the part of GitHub's API that we can send the access token to to take actions on behalf of the user (e.g. asking about their profile).
Source: Introduction to OAuth 2.0 and OpenID Connect (PowerPoint slides) - PragmaticWebSecurity.com
OpenID Connect (OIDC)
Again, GitHub doesn't seem to support this, but it's mentioned a lot online, so you may be curious to know what's going on here / what problem it solves / why GitHub doesn't support it.
The best explanation I've seen for why OpenID Connect was introduced and why it would be preferred over plain OAuth 2.0 for authentication is my own summary of a 2012 ThreadSafe blog post: Why use OpenID Connect instead of plain OAuth2?.
The short answer is that before OIDC existed, pure-frontend social login JavaScript libraries (like Facebook's) were using plain OAuth 2.0, but this method was open to an exploit where a malicious web app could have a user sign into their site (for example, using Facebook login) and then use the generated (Facebook) access token to impersonate that user on any other site that accepted that (Facebook) access token as a method of authentication. OIDC prevents that exploit.
This particular exploit is what people are referring to when they say "OAuth 2.0 is an authorization protocol, not an authentication protocol...OAuth says absolutely nothing about the user, nor does it say how the user proved their presence or even if they're still there.", which I saw mentioned over and over again while doing research on how to use OAuth 2.0 to implement social login, and which had me initially thinking that I needed to use OpenID Connect.
But GitHub doesn't have a pure-frontend social login JavaScript library, so it doesn't need to support OpenID Connect to address that exploit. You just need to make sure your app's back-end is keeping track of which GitHub access tokens it has generated rather than just trusting any valid GitHub access token it receives.
While doing research I came across HelloJS and wondered if I could use it to implement social login. From what I can tell, the answer is "not securely".
The first thing to understand is that when you use HelloJS, it is using the same authentication code flow I describe above, except HelloJS has its own back-end ("proxy") server set up to allow you to skip writing the back-end code normally needed to implement this flow, and the HelloJS front-end library allows you to skip writing all the front-end code normally needed.
The problem with using HelloJS for social login is the back-end server/proxy part: there seems to be no way to prevent the kind of attack that OpenID Connect was created to prevent: the end result of using HelloJS seems to be a GitHub access token, and there seems to be no way for your app's back-end to tell whether that access token was created by the user trying to log into your app or if it was created when the user was logging into some other malicious app (which is then using that access token to send requests to your app, impersonating the user).
If your app doesn't use a back-end then you could be fine, but most apps do rely on a back-end to store user-specific data that should only be accessible to that user.
You could get around this problem if you were able to query the proxy server to double-check which access tokens it had generated, but HelloJS doesn't seem to have a way to do this out-of-the-box, and if you decide to create your own proxy server so that you can do this, you seem to be ending up in a more-complicated situation than if you'd just avoided HelloJS from the beginning.
HelloJS instead seems to be intended for situations where your front-end just wants to query the GitHub API on behalf of the user to get information about their account, like their user details or their list of repositories, with no expectation that your back-end will be using the user's GitHub access token as a method for that user to access their private information on your back-end.
To implement the "web application flow" I used the following article as a reference, although it didn't perfectly map to what I needed to do with GitHub: OpenID Connect Client by Example - Codeburst.io
Keep in mind that this guide is for implementing the OpenID Connect authentication flow, which is similar-to-but-not-the-same-as the flow we need to use for GitHub.
The code here was especially helpful for getting my front-end code working properly.
GitHub does not allow for the use of a "nonce" as described in this guide, because that is a feature specific to (some implementations of?) OpenID Connect, and GitHub's API does not support the use of a nonce in the same way that Google's API does.
To implement the "device flow" I used the following article as inspiration: Using the OAuth 2.0 device flow to authenticate users in desktop apps
The key quote is this: "Basically, when you need to authenticate, the device will display a URL and a code (it could also display a QR code to avoid having to copy the URL), and start polling the identity provider to ask if authentication is complete. You navigate to the URL in the browser on your phone or computer, log in when prompted to, and enter the code. When you’re done, the next time the device polls the IdP, it will receive a token: the flow is complete."
Example code
The app I'm working on uses Vue + Quasar + TypeScript on the front-end, and Python + aiohttp on the back-end. Obviously you may not be able to use the code directly, but hopefully using it as a reference will give you enough of an idea of what the finished product should look like that you can more-quickly get your own code working.
Because of Stack Overflow's post length limits, I can't include the code in the body of this answer, so instead I'm linking the code in individual GitHub Gists.
App.vue
This is the 'parent component' which the entire front-end application is contained within. It has code that handles the situation during the "web application flow" where the user has been redirected by GitHub back to our application after authorizing our application. It takes the authorization code from the URL query parameters and sends it to our application's back-end, which in turn sends the authorization code to GitHub in exchange for the access token and refresh token.
axios.ts
This is most of the code from axios.ts. This is where I put the code that adds the GitHub access token to all requests to our app's back-end (if the front-end finds such a token in localStorage), as well as the code that looks at any responses from our app's back-end to see if the access token has been refreshed.
auth.py
This is the back-end file that contains all the routes used during the login process for both the "web application flow" and the "device flow". If the route URL contains "oauth" it's for the "web application flow", and if the route URL contains "device" it's for the "device flow"; I was just following GitHub's example there.
middleware.py
This is the back-end file that contains the middleware function that evaluates all incoming requests to see if the presented GitHub access token is one in our app's database, and hasn't yet expired. The code for refreshing the access token is in this file.
Login.vue
This is the front-end component that displays the "Login page". It has code for both the "web application flow" as well as the "device flow".
Summary of the two login flows as implemented in my application:
The web application flow
The user goes to http://mywebsite.com/
The front-end code checks whether there's an access_token localStorage variable (which would indicate the user has already logged in), and doesn't find one, so it redirects the user to the /login route.
See App.vue:mounted() and App.vue:watch:authenticated()
At the Login page/view, the user clicks the "Sign in with GitHub" button.
The front-end sets a random state localStorage variable, then redirects the user to GitHub's OAuth app authorization page with our app's client ID and the random state variable as URL query parameters.
See Login.vue:redirectUserToGitHubWebAppFlowLoginLink()
The user signs into GitHub (if they're not already signed in), authorizes our application, and is redirected back to http://mywebsite.com/ with an authentication code and the state variable as URL query parameters.
The app is looking for those URL query parameters every time it loads, and when it sees them, it makes sure the state variable matches what it stored in localStorage, and if so, it POSTs the authorization code to our back-end.
See App.vue:mounted() and App.vue:sendTheBackendTheAuthorizationCodeFromGitHub()
Our app's back-end receives the POSTed authorization code and then very quickly:
Note: the steps below are in auth.py:get_web_app_flow_access_token_and_refresh_token()
It sends the authorization code to GitHub in exchange for the access token and refresh token (as well as their expiration times).
It uses the access token to query GitHub's "/user" endpoint to get the user's GitHub id, email address, and name.
It looks in our database to see if we have a user with the retrieved GitHub id, and if not, creates one.
It creates a new "oauth_tokens" database record for the newly-retrieved access tokens and associates it with the user record.
Finally, it sends the access token to the front-end in the response to the front-end's request.
The front-end receives the response, sets an access_token variable in localStorage, and sets an authenticated Vue variable to true, which the app is constantly watching out for, and which triggers the front-end to redirect the user from the "login" view to the "app" view (i.e. the part of the app that requires the user to be authenticated).
See App.vue:sendTheBackendTheAuthorizationCodeFromGitHub() and App.vue:watch:authenticated()
The device flow
The user goes to http://mywebsite.com/
The front-end code checks whether there's an access_token localStorage variable (which would indicate the user has already logged in), and doesn't find one, so it redirects the user to the /login route.
See App.vue:mounted() and App.vue:watch:authenticated()
At the Login page/view, the user clicks the "Sign in with GitHub" button.
The front-end sends a request to our app's back-end asking for the user code that the user will enter while signed into their GitHub account.
See Login.vue:startTheDeviceLoginFlow()
The back-end receives this request and:
See auth.py:get_device_flow_user_code()
Sends a request to GitHub asking for a new user_code.
Creates an asynchronous task polling GitHub to see if the user has entered the user_code yet.
Sends the user a response with the user_code and device_code that it got from GitHub.
The front-end receives the response from our app's back-end and:
It stores the user_code and device_code in Vue variables.
See Login.vue:startTheDeviceLoginFlow()
The device_code is also saved to localStorage so that if the user closes the browser window that has the "log in" page open and then opens up a new one, they won't need to restart the login process.
It displays the user_code to the user.
See Login.vue in the template code block starting <div v-if="deviceFlowUserCode">
It shows a button that will open the GitHub URL where the user can enter the user_code (it will open the page in a new tab).
It shows a QR code that links to the same GitHub link, so that if the user is using the application on a computer and wants to enter the code on their phone, they can do that.
The app uses the received device_code to set a deviceFlowDeviceCode variable. A separate part of the code in the app is constantly checking to see if that variable has been set, and when it sees that it has, it begins polling the back-end to see if the back-end has received the access_token yet from GitHub.
See Login.vue:watch:deviceFlowDeviceCode() and Login.vue:repeatedlyPollTheBackEndForTheAccessTokenGivenTheDeviceCode()
The user either clicks the aforementioned button or scans the QR code with their phone, and enters the user code at https://github.com/login/device while logged into their GitHub account, either on the same device this application is running on or some other device (like their phone).
The back-end, while polling GitHub every few seconds as previously mentioned, receives the access_token and refresh_token, and as mentioned while describing the "web app flow", sends a request to GitHub's "/user" endpoint to get user data, then gets or creates a user db record, and then creates a new oauth_tokens db record.
See auth.py:_repeatedly_poll_github_to_check_if_the_user_has_entered_their_code()
The front-end, while polling our application's back-end every few seconds, finally receives a response from the back-end with the access_token, sets an access_token variable in localStorage, redirects the user to the "app" view (i.e. the part of the app that requires the user to be authenticated).
See Login.vue:repeatedlyPollTheBackEndForTheAccessTokenGivenTheDeviceCode()
This is a summary of an issue I filed directly with expo (it ws closed but I have asked for it to be reopened):
This issue happens whether using AuthSession.startAsync,
AppAuth.authAsync or WebBrowser.openAuthSessionAsync on iOS in
local development and published release (expo managed). Haven't tried
on standalone build yet.
Steps to Reproduce
user presses 'sign in' button, (app calls one of the above methods to kick start authentication session with a Salesforce oauth provider)
user enters credentials successfully
app goes through oauth redirects and returns user to our app and we get our access token.
user presses 'sign out' button (app calls revoke endpoint for token, then calls server endpoint to delete any browser cookie sessions for given account reference)
app navigates to sign in screen
user presses 'sign in' again (app calls the same method from above to start the authentication session with Salesforce oauth provider again)
instead of opening the sign in page, the app redirects itself back with an access token as if the user had successfully entered their credentials, even though any cookies/session data the browser stores should be invalid and necessitate a sign in.
Expected Behaviour
steps 1 - 5 are all as expected. Step six should be
app redirects to Salesforce oauth provider sign in page, in unauthenticated state (ie no cookie or session data that was previously stored is still valid)
user is required to re-enter their credentials
oauth flow takes over and redirects the user into the app if the credentials were correct.
Actual Behavior
as per initial steps where the user is not even asked to enter their credentials (step 6):
instead of opening the sign in page, the app redirects itself back with an access token as if the user had successfully entered their credentials, even though any cookies/session data the browser stores should be invalid and necessitate a sign in.
Reproducible Demo
The code is in a private repo so I can't share details of it, but it's a very standard oauth flow, and seeing it's happening in all three of the method calls from the top suggests to me that it may be due to something in the WebBrowser.openAuthSessionAsync implementation. I have seen on the apple developer docs that SFAuthenticationSession has been deprecated in favour of ASWebAuthenticationSession. My understanding is that this (SFAuthenticationSession) is the browser used by expo's WebBrowser and the wrappers mentioned above (AppAuth and AuthSession) for the oauth interactions. I also see that it mentions it's for a one-time login, which perhaps explains why it would hold onto any session data and jump to the conclusion of re-authenticating without directly seeking credentials from the user, but it seems unhelpful to store a cookie without validating it, which is what appears to be the end result.
Notes
Essentially this is making it impossible for a user to sign out of our app, because the system browser, that we don't have control over, is keeping track of their authentication despite the session value no longer being valid against the server.
I've seen other people looking to find ways to clear cookies from the system browser, which may be what this issue relates to, though it doesn't appear to be possible to access the auth session's browser cookies in any way. This comment on a GitHub issue is exactly what I'm experiencing and need to find a solution to.
I would like users to be able to sign out, and then when they sign back in again they should have to enter their credentials again. Does anyone have any thoughts as to how this might be possible?
On iOS, it's now possible to pass in the following config to WebBrowser.openAuthSessionAsync to essentially treat it as incognito and ensure it doesn't retain any cookies. The effect is that the user will have to re-authenticate each time (even if there session is still active). I'm not aware of a similar approach for Android, however.
Code
const browserOptions = {
preferEphemeralSession: true
}
result = await WebBrowser.openAuthSessionAsync(authUrl, redirect, browserOptions)
I am following this guide (https://learn.microsoft.com/en-us/skype-sdk/ucwa/authenticationusingazuread) in order to access Skype for Business. Everything goes fine till the last part but let's do step by step. I am building my .net console application to do this but in order to explain you properly the problem I am having I will show you directly the http calls through Insomnia (software used to make http calls).
Step 1:
GET request towards https://webdir.online.lync.com/autodiscover/autodiscoverservice.svc/root
I hit 200 and as answer I receive this:
Step 2:
I use the user link.
So I send an http request to https://webdir1e.online.lync.com/Autodiscover/AutodiscoverService.svc/root/oauth/user and I get a 401 Unauthorized (everything still correct).
In the header of the answer it points me to the Identity Provider to ask for authorization (authorization_uri)
Step 3: I use that link to authorize my app, which has its own client_Id (that I hide in the following screenshot).
This is how I compose the call:
If I send this http request I get redirected to the page where it asks my personal login and by inserting my credentials I succesfully login and hit 404, where in the answer I receive back my access token.
Step 5: I use the access token towards the same AutodiscoverService link of step 1. This is to register my application. I hit 200 and I receive back the link to access Skype for Business.
Finally (and this is where things go wrong) I send a POST request towards the applications link with the Bearer token, and I receive a 403 Forbidden. I think I am following correctly the guide but I can't figure out why I can access the resource at the last step.
EDIT:
The permissions are granted. I hide the name since it contains the name of my company. But it is the same of the domain of my login.
So the token you generated authorizes you to access resources at https://webdir1e.online.lync.com which you've done to fetch a new set of resources including the "application" resouce which is on a DIFFERENT host: https://webpooldb41e14.infra.lync.com.
You actually have to get another OAuth token now which authorizes you for the application resource and then you can POST to that to generate your session in UCWA.
As a side note... If you've defined your own single-tenant application in Azure that has been granted rights to SkypeForBusinessOnline then I think you should be targeting authorization and authentication endpoints of the form:
https://login.microsoftonline.com/{tenantID}/oauth2/v2.0/authorize
https://login.microsoftonline.com/{tenantID}/oauth2/v2.0/token
Also I should add, if you're trying to write a trusted secure client that users in your company will use I would suggest looking up the Resource Owner Password Credentials auth flow. It allows you to directly hit the token endpoint I mentioned above and exchange username/password credentials for an access token. Then you can manage auto-discovery and application creation easily under the hood without getting re-directed back and forth to Azure.
https://learn.microsoft.com/mt-mt/azure/active-directory/develop/v2-oauth-ropc
The Google+ Sign-In button bears a striking similarity to the Facebook Login API, and I like that.
The Facebook JS SDK has a signed_request parameter that's provided on the client side but which can be passed to my server, verifying that client-side authentication has taken place. It's cryptographically signed by Facebook, which allows me to verify that the client is logged in without talking to the Facebook on the server side.
Is there a way to do something similar with the G+ JS API? Specifically, I want to do client-side authentication, then POST some data to my server and verify that the client really is logged in to Google, without initiating a server-side request to Google.
(I want this because I only want to use the sign in button as a registration mechanism; I don't want to post to Google Plus or get the user's list of friends or anything like that, which would normally require a full access token.)
Google+ does not make requests to your application on the user's behalf at this time, outside of a callback URL set as part of a vanilla OAuth 2.0 flow.
When receiving a new token or authorization code, you should make the tokeninfo request server-side in order to verify that the token you've received is legitimate, and for the intended user.
I'm not sure which platform your server is using, so I can't paste the relevant code, but please see here for a code sample.
So, actually there is a pretty good match for that parameter, the id_token that is returned along with the access_token. It's a signed json web token that includes a userid, the client ID and so on. It sounds like this would address your use case! Take a look at http://android-developers.blogspot.nl/2013/01/verifying-back-end-calls-from-android.html this blog post by Tim Bray - it's Android focused, but the same logic pretty much works for any client.
Once you get this, you know its valid at the point of delivery, just liked a signed_request. Of course in either case if the user signs out or revokes access to your app the access token may no longer be valid for making calls.
I've been reading lots of documentation about Google API access and OAuth flow using it but I don't seem to get it working in my mind, so I want to get some help first in order to have a clear idea about how it works then I can code it using the corresponding API.
What I want to achieve is feed a Java application running in a PC with specific Google user data, like localization through Google Latitude API. In order to get this, OAuth must be used, so I need getting the user consent, then access the user data from the application running in my computer, and I don't know how to manage this.
I've already registered my application with the Google APIs Console and enabled the Google Latitude module. I've also tried the Latitude console application here and it works properly (a browser tab opened asking for a Google user; I entered it and I got the location data), but I'm having problems when trying to adapt the program flow to my needs.
In my application, the 'remote' user is supposed to send a request (a custom JSON message) to the server asking for service enable/disable, like allowing the server to track his/her position through Latitude. Then, AFAIK, the server should send to the user a URL so the user can give the consent, but I don't know how to get this URL and how the server realizes about this consent and gets the token (automatically? Google tracks this authorization process?). Once my server gets the specific user token, then I should be ready to get service data for that user using the received token.
As I said before, I've tried according to different references, but as the documentation seems to be really scattered and much of it is already deprecated, I've been unable to get it working.
Judging from your description, the installed app OAuth2 flow seems to be the right one for you.
At some point, presumably when a user is installing your desktop app, you should fire up a browser - either embedded one in your app or the default browser - and sent them to this Google OAuth2 endpoint. In your request, fill out all the parameters as required by the doc: Latitude API scope, client_id, etc. Google, as an authorization server, will take care of user authentication, session selection, and user consent. If the user grants access to her data to your API, you will receive an authorization code either in the title of the browser window or at a localhost port.
Once you have the code, you can exchange it for an access token and a refresh token. The access token is what you need to call the API and access the user's data. It is short lived though - check the expired_in parameter in the response, I believe it is 3600 sec. - so you will need to periodically ping the token endpoint with your long lived refresh token and exchange it for an access token.
You can find a more thoroough description of this flow in the doc linked above.