You can use the Auth0 Authentication API to create server-side web applications that uses OAuth 2.0 authorization to authenticate users.

Auth0 exposes OAuth 2.0 endpoints for authenticating any user. You can redirect the user from your web application to these endpoints in the web browser. Auth0 will handle the authentication of the user, and then redirect the user back to the redirect_uri (also referred to as the Callback URL), returning an authorization_code in the query string parameters of the Callback URL. This authorization_code can then be exchanged for an ID Token which contains the identity of the user.

The OAuth 2.0 Authorization Framework allows for different kinds of authorization flows (called Grant Types) depending on the type of application. The flow used for Server-side Web applications is known as the Authorization Code flow.

The Authorization Code flow is initiated by redirecting the user in the web browser to the Auth0 /authorize endpoint. Auth0 will then display the Auth0 Lock dialog, allowing the user to enter their credentials or alternatively sign in with any other configured Identity Provider.

After the user has authenticated, Auth0 will redirect the browser back to the Redirect URI (also called Callback URL), passing along an authorization_code parameter in the query string of the Callback URL. This code can then be exchanged for an ID Token by making a request to the /oauth/token endpoint.

The ID Token is a JSON Web Token (JWT) and contains various attributes - referred to as Claims - regarding the user, such as the user's name, email address, profile picture and so on.. The ID Token can be decoded to extract the claims and you are free to use these inside of your application, to display a user's name and profile image for example.

1. The Application initiates the flow and redirects the user to the Authorization Server.
2. The user authenticates.
3. The Authorization Server redirects to the redirect_uri with an authorization_code in the query string.
4. The Application sends the authorization_code together with the redirect_uri and the Client Id/Client Secret to the Authorization Server.
5. The Authorization Server validates this information and returns an ID Token.

The first thing you need to do is to create a new application in Auth0. An Auth0 application maps to your application and allows it to use Auth0 for authentication.

Navigate to the Auth0 Dashboard and click on the Applications menu option on the left. Create a new Application by clicking on the Create Application button.

The Create Application window will open, allowing you to enter the name of your new application. Choose Regular Web Applications as the Application Type and click on the Create button to create the new application.

Once the application has been created you can navigate to the Settings tab of the application and in the Allowed Callback URLs field add a URL where Auth0 must redirect to after the user has authenticated, such as https://YOUR_APP/callback.

This URL must be part of your application, as your application will need to retrieve the code and exchange it for the ID Token.

The URL used when authenticating a user is https://YOUR_DOMAIN/authorize. This is the initial endpoint to which a user must be redirected. This will handle checking whether any SSO session is active, authenticating the user and also potentially redirect the user directly to any Identity Provider to handle authentication.

This endpoint supports the following query string parameters:

After the user has authenticated, Auth0 will call back to the URL specified in the redirect_uri query string parameter which was passed to the /authorize endpoint. When calling back to this URL, Auth0 will pass along an access_token in the code query string parameter of the URL, such as

https://YOUR_APP/callback?code=2OKj...

You application will need to handle the request to this callback URL, extract the access_code from the code query string parameter and call the /oauth/token endpoint of the Auth0 Authentication API in order to exchange the access_code for the ID Token:

curl --request POST \
  --url 'https://YOUR_DOMAIN/oauth/token' \
  --header 'content-type: application/json' \
  --data '{"grant_type":"authorization_code","client_id": "YOUR_CLIENT_ID","client_secret": "YOUR_CLIENT_SECRET","code": "YOUR_AUTHORIZATION_CODE","redirect_uri": "https://YOUR_APP/callback"}'

var client = new RestClient("https://YOUR_DOMAIN/oauth/token");
var request = new RestRequest(Method.POST);
request.AddHeader("content-type", "application/json");
request.AddParameter("application/json", "{\"grant_type\":\"authorization_code\",\"client_id\": \"YOUR_CLIENT_ID\",\"client_secret\": \"YOUR_CLIENT_SECRET\",\"code\": \"YOUR_AUTHORIZATION_CODE\",\"redirect_uri\": \"https://YOUR_APP/callback\"}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io/ioutil"
)

func main() {

	url := "https://YOUR_DOMAIN/oauth/token"

	payload := strings.NewReader("{\"grant_type\":\"authorization_code\",\"client_id\": \"YOUR_CLIENT_ID\",\"client_secret\": \"YOUR_CLIENT_SECRET\",\"code\": \"YOUR_AUTHORIZATION_CODE\",\"redirect_uri\": \"https://YOUR_APP/callback\"}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("content-type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := ioutil.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://YOUR_DOMAIN/oauth/token")
  .header("content-type", "application/json")
  .body("{\"grant_type\":\"authorization_code\",\"client_id\": \"YOUR_CLIENT_ID\",\"client_secret\": \"YOUR_CLIENT_SECRET\",\"code\": \"YOUR_AUTHORIZATION_CODE\",\"redirect_uri\": \"https://YOUR_APP/callback\"}")
  .asString();

var request = require("request");

var options = { method: 'POST',
  url: 'https://YOUR_DOMAIN/oauth/token',
  headers: { 'content-type': 'application/json' },
  body: 
   { grant_type: 'authorization_code',
     client_id: 'YOUR_CLIENT_ID',
     client_secret: 'YOUR_CLIENT_SECRET',
     code: 'YOUR_AUTHORIZATION_CODE',
     redirect_uri: 'https://YOUR_APP/callback' },
  json: true };

request(options, function (error, response, body) {
  if (error) throw new Error(error);

  console.log(body);
});

#import <Foundation/Foundation.h>

NSDictionary *headers = @{ @"content-type": @"application/json" };
NSDictionary *parameters = @{ @"grant_type": @"authorization_code",
                              @"client_id": @"YOUR_CLIENT_ID",
                              @"client_secret": @"YOUR_CLIENT_SECRET",
                              @"code": @"YOUR_AUTHORIZATION_CODE",
                              @"redirect_uri": @"https://YOUR_APP/callback" };

NSData *postData = [NSJSONSerialization dataWithJSONObject:parameters options:0 error:nil];

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"https://YOUR_DOMAIN/oauth/token"]
                                                       cachePolicy:NSURLRequestUseProtocolCachePolicy
                                                   timeoutInterval:10.0];
[request setHTTPMethod:@"POST"];
[request setAllHTTPHeaderFields:headers];
[request setHTTPBody:postData];

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request
                                            completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
                                                if (error) {
                                                    NSLog(@"%@", error);
                                                } else {
                                                    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *) response;
                                                    NSLog(@"%@", httpResponse);
                                                }
                                            }];
[dataTask resume];

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => "https://YOUR_DOMAIN/oauth/token",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => "{\"grant_type\":\"authorization_code\",\"client_id\": \"YOUR_CLIENT_ID\",\"client_secret\": \"YOUR_CLIENT_SECRET\",\"code\": \"YOUR_AUTHORIZATION_CODE\",\"redirect_uri\": \"https://YOUR_APP/callback\"}",
  CURLOPT_HTTPHEADER => array(
    "content-type: application/json"
  ),
));

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

import http.client

conn = http.client.HTTPSConnection("")

payload = "{\"grant_type\":\"authorization_code\",\"client_id\": \"YOUR_CLIENT_ID\",\"client_secret\": \"YOUR_CLIENT_SECRET\",\"code\": \"YOUR_AUTHORIZATION_CODE\",\"redirect_uri\": \"https://YOUR_APP/callback\"}"

headers = { 'content-type': "application/json" }

conn.request("POST", "/YOUR_DOMAIN/oauth/token", payload, headers)

res = conn.getresponse()
data = res.read()

print(data.decode("utf-8"))

require 'uri'
require 'net/http'

url = URI("https://YOUR_DOMAIN/oauth/token")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
http.verify_mode = OpenSSL::SSL::VERIFY_NONE

request = Net::HTTP::Post.new(url)
request["content-type"] = 'application/json'
request.body = "{\"grant_type\":\"authorization_code\",\"client_id\": \"YOUR_CLIENT_ID\",\"client_secret\": \"YOUR_CLIENT_SECRET\",\"code\": \"YOUR_AUTHORIZATION_CODE\",\"redirect_uri\": \"https://YOUR_APP/callback\"}"

response = http.request(request)
puts response.read_body

import Foundation

let headers = ["content-type": "application/json"]
let parameters = [
  "grant_type": "authorization_code",
  "client_id": "YOUR_CLIENT_ID",
  "client_secret": "YOUR_CLIENT_SECRET",
  "code": "YOUR_AUTHORIZATION_CODE",
  "redirect_uri": "https://YOUR_APP/callback"
]

let postData = NSJSONSerialization.dataWithJSONObject(parameters, options: nil, error: nil)

var request = NSMutableURLRequest(URL: NSURL(string: "https://YOUR_DOMAIN/oauth/token")!,
                                        cachePolicy: .UseProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.HTTPMethod = "POST"
request.allHTTPHeaderFields = headers
request.HTTPBody = postData

let session = NSURLSession.sharedSession()
let dataTask = session.dataTaskWithRequest(request, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    println(error)
  } else {
    let httpResponse = response as? NSHTTPURLResponse
    println(httpResponse)
  }
})

dataTask.resume()

The response from /oauth/token contains an access_token, id_token and token_type values (and also potentially a refresh_token), for example:

{
  "access_token": "AP16...",
  "id_token": "eyJ0...",
  "token_type": "Bearer"
}

The token_type will be set to Bearer and the id_token will be a JSON Web Token (JWT) containing information about the user. You will need to decode the ID Token in order to read the claims (or attributes) of the user. The JWT section of our website contains more information about the structure of a JWT.

You can refer to the libraries section on the JWT.io website in order to obtain a library for your programming language of choice which will assist you in decoding the ID Token.

Once the JWT is decoded, you can extract the information about the user from the Payload of the ID Token. This is a JSON structure and will contain the claims (attributes) about the user as well as some other metadata.

An example payload for an ID Token may look something like this:

{
  "name": "Jerrie Pelser",
  "email": "jerrie@j...",
  "picture": "https://s.gravatar.com/avatar/6222081fd7dcea7dfb193788d138c457?s=480&r=pg&d=https%3A%2F%2Fcdn.auth0.com%2Favatars%2Fje.png",
  "iss": "https://auth0pnp.auth0.com/",
  "sub": "auth0|581...",
  "aud": "xvt...",
  "exp": 1478113129,
  "iat": 1478077129
}

The payload above contains the following claims:

The exact claims contained in the ID Token will depend on the scope parameter you sent to the /authorize endpoint. In an ID Token issued by Auth0, the registered claims and the sub claim will always be present, but the other claims depends on the scope. You can refer to the examples below to see examples of how the scope influences the claims being returned.

Auth0 will assist you in authenticating a user, but it is up to you to keep track in your application of whether or not a user is logged in. You can use a cookie or other session storage to keep track of whether a user is logged in or not, and also to store the claims of the user which was extracted from the ID Token.

You can then use those claims inside of your application to display the user's information or otherwise personalize the user's experience.

The following is the most basic request you can make to the /authorize endpoint. It will display the Lock screen and allow a user to sign in with any of the configured connections.

https://YOUR_DOMAIN/authorize
  ?response_type=code
  &client_id=YOUR_CLIENT_ID
  &redirect_uri=https://YOUR_APP/callback

After the user has authenticated, they will be redirected back to the redirect_uri with the access_code in the code query string parameter:

https://YOUR_APP/callback?code=2OKj...

You can then exchange the access_code for an ID Token. This is an example of the decoded payload of the ID Token which will be returned:

{
  "iss": "https://auth0pnp.auth0.com/",
  "sub": "auth0|581...",
  "aud": "xvt9...",
  "exp": 1478112929,
  "iat": 1478076929
}

You can request a user's name and profile picture by requesting the name and picture scopes.

https://YOUR_DOMAIN/authorize
  ?response_type=code
  &client_id=YOUR_CLIENT_ID
  &redirect_uri=https://YOUR_APP/callback
  &scope=openid%20name%20picture

After the user has authenticated, they will be redirected back to the redirect_uri with the access_code in the code query string parameter:

https://YOUR_APP/callback?code=2OKj...

You can then exchange the access_code for an ID Token. The name and profile picture will be available in the name and picture claims of the returned ID Token:

{
  "name": "jerrie@...",
  "picture": "https://s.gravatar.com/avatar/6222081fd7dcea7dfb193788d138c457?s=480&r=pg&d=https%3A%2F%2Fcdn.auth0.com%2Favatars%2Fje.png",
  "iss": "https://auth0pnp.auth0.com/",
  "sub": "auth0|581...",
  "aud": "xvt...",
  "exp": 1478113129,
  "iat": 1478077129
}

You can send a user directly to the GitHub authentication screen by passing the value of github to the connection parameter. Note that we also request the openid, name, picture and email scopes:

https://YOUR_DOMAIN/authorize
  ?response_type=code
  &client_id=YOUR_CLIENT_ID
  &redirect_uri=https://YOUR_APP/callback
  &scope=openid%20name%20picture%20email
  &connection=github

After the user has authenticated, they will be redirected back to the redirect_uri with the ID Token and token_type passed as parameters in the hash fragment:

After the user has authenticated, they will be redirected back to the redirect_uri with the access_code in the code query string parameter:

https://YOUR_APP/callback?code=2OKj...

You can then exchange the access_code for an ID Token. The user's name and profile picture and email address will be available in the name, picture and email claims of the returned ID Token. You will also notice that the sub claim contains the User's unique ID returned from GitHub:

{
  "name": "Jerrie Pelser",
  "picture": "https://avatars.githubusercontent.com/u/1006420?v=3",
  "email": "jerrie@...",
  "email_verified": true,
  "iss": "https://auth0pnp.auth0.com/",
  "sub": "github|100...",
  "aud": "xvt...",
  "exp": 1478114742,
  "iat": 1478078742
}