keycloak-scim/topics/sso-protocols/oidc.adoc

[[_oidc]]

=== Open ID Connect

link:http://openid.net/connect/[Open ID Connect] (OIDC) is an authentication protocol that is an extension of link:https://tools.ietf.org/html/rfc6749[OAuth 2.0].
While OAuth 2.0 is only a framework for building authorization protocols and is mainly incomplete, OIDC is a full-fledged authentication and authorization
protocol.  OIDC also makes heavy use of the link:https://jwt.io[Json Web Token] (JWT) set of standards.  These standards define a
identity token JSON format and ways to digitially sign and encrypt that data in a compact and web-friendly way.

There is really two types of use cases when using OIDC.  The first is an application that asks the {{book.project.name}} server to authenticate
a user for them.  After a successful login, the application will receive an _identity token_ and an _access token_.  The _identity token_
contains information about the user such as username, email, and other profile information.  The _access token_ is digitially signed by
the realm and contains access information (like user role mappings) that the application can use to determine what resources the user
is allowed to access on the application.

The second type of use cases is that of a client that wants to gain access to remote services.  In this case, the client asks {{book.project.name}}
to obtain an _access token_ it can use to invoke on other remote services on behalf of the user.  {{book.project.name}} authenticates the user
then asks the user for consent to grant access to the client requesting it.  The clien then receives the _access token_.  This _access token_
is digitally signed by the realm.  The client can make REST invocations on remote services using this _access token_.  The REST service
extracts the _access token_, verifies the signature of the token, then decides based on access information within the token whether or not to process
the request.

[[_oidc-auth-flows]]

==== OIDC Auth Flows

OIDC has different ways for a client or application to authenticate a user and receive an _identity_ and _access_ token.  Which
path you use depends greatly on the type of application or client requesting access.  All of these flows are described in the
OIDC and OAuth 2.0 specifications so only a brief overview will be provided here.

===== Authorization Code Flow

This is a browser-based protocol and what we recommend you use to authenticate and authorize browser-based applications.  It makes
heavy use of browser redirects to obtain an _identiy_ and _access_ token.  Here's a brief summary

. Browser visits application.  The application notices the user is not logged in, so it redirects the browser to {{book.project.name}}
  to be authenticated.  The application passes along a callback URL (a redirect URL) as a query parameter in this browser redirect
  that {{book.project.name}} will use when it finishes authentication.
. {{book.project.name}} authenticates the user and creates a one-time, very short lived, temporary code.  {{book.project.name}}
  redirects back to the application using the callback URL provided earlier and additionally adding the temporary code
  as a query parameter in the callback URL.
. The application extracts the temporary code and makes a background out of band REST invocation to {{book.project.name}}
  to exchange the code for an _identity_, _access_ and _refresh_ token.  Once this temporary code has been used once
  to obtain the tokens, it can never be used again.  This prevents potential reply attacks.

It is important to note that _access_ tokens are usually short lived and often expired after only minutes.  The additional _refresh_
token that was transmitted by the login protocol allows the application to obtain a new access token after it expires.  This
refresh protocol is important in the situation of a compromised system.  If access tokens are short lived, the whole system is only
vulnerable to a stolen token for the lifetime of the access token.  Future refresh token requests will fail if an admin
has revoked access.  This makes things more secure and more scalable.

[[_confidential-clients]]
Another important aspect of this flow is the concept of a _public_ vs. a _confidential_ client.  _Confidential_ clients are required
to provide a client secret when they exchange the temporary codes for tokens.  _Public_ clients are not required to provide this client secret.
_Public_ clients are perfectly fine so long as HTTPS is strictly enforced and you are very strict about what redirect URIs are registered for the
client.  HTML5/Javascript clients actually always have to be _public_ clients because there is no way to transmit the client secret to them in a secure
manner.  Again, this is ok so long as you use HTTPS and strictly enforce redirect URI registration.  This guide goes more detail
into this in the <<fake/../../client.adoc,Client>> chapter.

===== Implicit Flow

This is a browser-based protocol that is similar to Authorization Code Flow except there are fewer requests and no refresh tokens involved.
We do not recommend this flow as there remains the possiblity of _access_ tokens being leaked in the browser history as tokens are transmitted
via redirect URIs (see below).  Also, since this flow doesn't provide the client with a refresh token, access tokens would either have to
be long-lived or users would have to re-authenticate when they expired.  This flow is supported because its in the OIDC and OAuth 2.0 specification.
Here's a brief summary of the protocol:

. Browser visits application.  The application notices the user is not logged in, so it redirects the browser to {{book.project.name}}
  to be authenticated.  The application passes along a callback URL (a redirect URL) as a query parameter in this browser redirect
  that {{book.project.name}} will use when it finishes authentication.
. {{book.project.name}} authenticates the user and creates an _identity_ and _access_ token.  {{book.project.name}}
  redirects back to the appliciation using the callback URL provided earlier and additionally adding the _identity_ and
  _access_ tokens as query parameters in the callback URL.
. The application extracts the the _identity_ and _access_ tokens from the callback URL.

===== Resource Owner Password Credentials Grant (Direct Grants)

This is referred to in the Admin Console as _Direct Grants_ This is used by REST clients that want to obtain a token on behalf of a user.  It is one HTTP POST request that contains
the credentials of the user as well as the id of the client and the client's secret (if it is a confidential client).  The user's credentials
are sent within form parameters.  The HTTP response contains
_identity_, _access_, and _refresh_ tokens.

===== Client Credentials Grant

This is also used by REST clients, but instead of obtaining a token that works on behalf
of an external user, a token is created based on the metadata and permissions of a service account that is associated with the client.

====  {{book.project.name}} Server OIDC URI Endpoints

Here's a list of OIDC endpoints that the {{book.project.name}} publishes.  These URLs are useful if you are using a non-{{book.project.name}} client adapter to
talk OIDC with the auth server.  These are all relative URLs and the root of the URL being the HTTP(S) protocol, hostname, and usually path prefixed with
_/auth_:  i.e. https://localhost:8080/auth

/realms/\{realm-name}/protocol/openid-connect/token::
  This is the URL endpoint for obtaining a temporary code in the Authorization Code Flow or for obtaining tokens via the
  Implicit Flow, Direct Grants, or Client Grants.
/realms/\{realm-name}/protocol/openid-connect/auth::
  This is the URL endpoint for the Authorization Code Flow to turn a temporary code into a token.
/realms/{realm-name}/protocol/openid-connect/logout::
  This is the URL endpoint for performing logouts.
/realms/\{realm-name}/protocol/openid-connect/userinfo::
  This is the URL endpoint for the User Info service described in the OIDC specification.

In all of these replace _\{realm-name}_ with the name of the realm.