OAuth terminology has been bothering me a long time now. Is OAuth Authorization as some would suggest or is it Authentication?
Correct me if I'm wrong but I have always read Authorization as being the act of allowing someone access to a resource yet OAuth doesn't seem to have any implementation that actually allows access to users to a given resource. All OAuth implementations talk about is providing a user a token (signed and sometimes encrypted). This token is then passed with every call to a back-end service endpoint where it is checked for validity, again not an OAuth concern.
Is OAuth Authentication (every article says it isn't) which I take it requires a user to provide credentials which in turn proves a user should/shouldn't have access?
So it seems that OAuth is not Authorization NOR Authentication since these have to be performed by other processes. So what the heck is it? Is it a process for communicating a token? Is it fluff word that really has no specific meaning?
It's hard to ask a question about this subject without sounding enigmatic and superstitious (ghosts and goblins) so I expect that answering this question won't be a simple thing either. Enter at your own risk.
OAuth is a specification for authorization
OAuth 2.0 is a specification for authorization, but NOT for authentication. RFC 6749, 3.1. Authorization Endpoint explicitly says as follows:
The authorization endpoint is used to interact with the resource owner
and obtain an authorization grant. The authorization server MUST first
verify the identity of the resource owner. The way in which the
authorization server authenticates the resource owner (e.g., username
and password login, session cookies) is beyond the scope of this
specification.
OAuth authentication?
Authentication deals information about "who one is". Authorization deals information about "who grants what permissions to whom". Authorization flow contains authentication as its first step. It is the reason people are often confused.
There are many libraries and services that use OAuth 2.0 for authentication. It is often called "social login" and It makes people more confused. If you see "OAuth authentication" (not "OAuth authorization"), it is a solution using OAuth for authentication.
OpenID Connect
OpenID 1.0 and OpenID 2.0 are old specifications for authentication. Those who made the specifications expected people to use OpenID for authentication. However, some people began to use OAuth 2.0 for authentication (not for authorization) and OAuth authentication has prevailed rapidly.
From a viewpoint of OpenID guys, authentication based on OAuth was not secure enough, but they had to admit that people preferred OAuth authentication. As a result, OpenID guys decided to define a new specification, OpenID Connect, on top of OAuth 2.0.
Yes, this has made people much more confused.
One-sentence definitions of OAuth 2.0 and OpenID Connect
OAuth 2.0 is a framework where a user of a service can allow a third-party application to access his/her data hosted in the service without revealing his/her credentials (ID & password) to the application.
OpenID Connect is a framework on top of OAuth 2.0 where a third-party application can obtain a user's identity information which is managed by a service.
(Sorry, these definitions are excerpts from the overview page of my company)
Definitions from a viewpoint of implementors
Authentication is a process to determine the subject (= unique identifier) of an end-user. There are many ways to determine the subject. ID & password, fingerprints, iris recognition, etc.
Authorization is a process to associate the subject with the requested permissions and the client application that requested the permissions. An access token represents the association.
See Also
Full-Scratch Implementor of OAuth and OpenID Connect Talks About Findings
Diagrams And Movies Of All The OAuth 2.0 Flows
Diagrams of All The OpenID Connect Flows
The Simplest Guide To OAuth 2.0
OAuth is an authorization protocol. It is not designed for authentication. Yes, there is a step in the OAuth process where the identity server authenticates a resource owner. The way it happens does not belong to the OAuth protocol. That is why OAuth does not concern itself about authentication.
OAuth performs authorization by giving an access token to a third party (service provider) and that party will be able to authorize access to the resource by presenting the token.
Let's say there is a requirement that a service provider wants to access resources (protected by an identity server) on behalf of the resource owner. So the resource owner will first authenticate and then will grant permission for the service provider to access specific resource. Then the identity server will issue an access token for service provider. Later the service provider can access the resource with that token.
Here, OAuth does not care about who is carrying the access token or trying to access the resources. It validates the access token, and lets the third party access the resources.
Related
I am confused about the use of OAuth 2.0 as an Authorization method and OpenID Connect as an Authentication method.
Based on my knowledge OAuth 2.0 is only an Authorization method. In other words, this is the process to request an ACCESS_TOKEN and RECEIVE this ACCESS_TOKEN, like depicted in the image below in yellow ellipse: (simplified)
Before an OAuth 2.0 Client retrieves an ACCESS_TOKEN from an Authorization Server this Server should verify if the User allows it and this is an Authentication Process that OAuth 2.0 does not care about.
When OpenID Connect is included in the mix it allows for an Authentication Method as well, but in my knowledge OpenID Connect just adds a "Claim" in the JWT Token that holds information about user that is using the service, like: email, name and others.
My questions are:
Why not ignore OpenID Connect and just add more "claims" in OAuth
2.0 to get information about users?
Is my description of the flows correct?
OpenID Connect does not merely "add a claim in JWT Token" but:
it introduces a completely new token (id_token) with radically different
semantics than the OAuth 2.0 access_token and a standardized format that is understood by the Client as opposed to the access_token which is opaque to the Client
it "twists" the role of the Client, now becoming the "audience" (or: intended recipient) of a token (i.e. the id_token) whilst the audience of the access_token is still a remote entity (aka. Resource Server) and the Client is only the "presenter" of the latter
The 2nd item is the primary source of confusion between OAuth 2.0 and OpenID Connect.
I don't know if your method will work or not but you're totally free to roll your own authentication. After all, that's what Facebook, GitHub and many others did by customizing oauth2. There ended up being so many oauth2 "authentication" methods that it was never plug and play if you wanted to change your provider. I believe that's why OpenID connect was introduced--a common way of connecting and reasoning about authentication while building on the established oauth2 pattern for authorization. Use OpenID connect or don't...but if you don't you'll be reinventing the wheel.
#sdoxee answers explains thing correctly. But I am adding bit more information for OP's understanding.
These days many identity providers (eg:- Azure AD) issue JWT based access tokens. These JWT access tokens do contain claims about end user as well as JWT related validation details (eg:- Token expiration). Here is the link for Azure AD OAuth 2 success response which highlights access token to be a JWT. Also, see JWT claims to see how they explain the claims. Samples are given below,
family_name : User’s last name or surname. The application can display this value.
given_name : User’s first name. The application can display this value.
One could think of building authentication on claims present in access token, but this is not sticking with protocol. And mostly claims and user information will be implementer specific. Also, by protocol definition, these two tokens (id and access) have two different audiences.
ID token is for client, for validation and for authentication.
Access token is for OAuth 2 protected endpoint.
Again, as #sdoxee highlight, use the correct protocol at correct place. Having claims in access token does not necessarily mean you should use them for authentication.
In case of OAuth 2.0 authorization code and implicit flow cases, on hitting the Authorization Url user is redirected to OAuth providers login page.
To avoid showing up the OAuth providers page in my application, can i make user to enter username and password in text fields and pass them as Authorization header of authorization Url and get back access_token from OAuth provider and use it for further requests ?
Is it legal, valid and feasible ?
Is it legal, valid and feasible ?
No. Not with the flow you are using right now. Implicit flow is not built for this purpose, so you cannot do it.
But, OAuth 2.0 provide you a dedicated flow for your requirement.
4.3. Resource Owner Password Credentials Grant
The resource owner password credentials grant type is suitable in
cases where the resource owner has a trust relationship with the
client, such as the device operating system or a highly privileged application.
As described in protocol, in this flow, your end user(resource owner) provide their credentials to client application. Client application call token endpoint with resource owner credentials to obtain access tokens.
Flow overview (From RFC6749)
Token request request (From RFC6749)
As specification mention, this flow is there to support old systems which are unable to fully utilise OAuth 2.0. For example clients which use basic authentication.
I've read a number of different write-ups on this now, but I'm still unclear as to the primary value that OpenID Connect provides on top of OAuth 2.0.
My understanding:
When receiving an access token via the OAuth 2.0 flow, the client does come to know that the user was authenticated by the authorization server. It seems like OpenID Connect is just adding an ID token with user information - but that information could be part of the access token or available through a protected resource (like a separate userDetails resource). That doesn't seem to justify the creation of OpenID Connect, so I'm sure that I'm missing something...
Thanks for your help!
Adding more details that are too long for a comment. Thanks much for your help so far.
I think I'm getting closer, thanks to your responses. So I reviewed this article: http://oauth.net/articles/authentication/. It says that "OAuth says absolutely nothing about the user". However, you are trusting that same service to authenticate the End-User before issuing an Access Token. In the "common pitfalls section", the article discusses why you can't use access token for authentication. I have the following issues with that in my understanding:
Access token as proof of authentication
The access token was proof of authentication at some prior point. If the Client does want to authenticate the user at some point after getting an access token, why not just repeat the existing Oauth flow with the current end-user trying to access the client?
Access of a protected resource as proof
Same as above - if the client requires authentication at any point, repeat the Oauth flow.
Injection of access tokens
Not clear how OpenID helps this
Lack of audience restriction
Why is it harder to hand a naive client a valid ID token along with the access token? Is this relevant at all to the server-side flow? And again, can repeat the OAuth flow if needed.
Injection of invalid user information
This seems to require a signature, not a separate token. If the OAuth flow takes place over HTTPS, is it adding any security for the identity provider to sign user details twice?
Different protocols for every potential identity provider
This seems fair, but it still seems strange if the only purpose would be standardization of the token used for user information.
An OAuth access token is opaque to the Client and could have been provided by anyone, which means that it is not necessarily handed to the Client by a logged in user. An attacker could provide an access token to the Client that it got from a different user in its own (not necessarily malicious) service. The ID token from OpenID Connect make sure that the user was logged in recently at the OP and provides information about that user that can be verified by the Client. Moreover the ID token is targeted specifically to your Client.
The differences are described pretty well in http://oauth.net/articles/authentication/
An ID token can be signed by the authentication server. A client application can verify the signature to confirm that the end-user has been authenticated by the very authentication server. Access token + protected resource call do not provide such a mechanism.
In addition, OpenID Connect has introduced other mechanisms related to authentication such as:
Authentication Context Class Reference
Maximum Authentication Age
sub claim in claims request parameter
to satisfy higher-level security requirements by governments.
Read OpenID Connect Core 1.0 and other related specifications. Also, you may find "Authorization interaction" helpful as a summary about what OpenID Connect has added to control end-user authentication.
OAuth 2.0 is about granting a third party limited access to a resource. The RFC starts with
The OAuth 2.0 authorization framework enables a third-party
application to obtain limited access to an HTTP service...
OpenID Connect is about establishing an end-user's identity. The OpenID Connect Core spec starts with
OpenID Connect 1.0 is a simple identity layer on top of the OAuth 2.0
protocol. It enables Clients to verify the identity of the End-User
based on the authentication performed by an Authorization Server...
In OAuth 2.0, when a resource server receives a request containing an access token, the resource server knows that the resource owner has granted a third party access to a resource. The access token represents this approval but it does not identify the third party who is presenting it.
If a company thinks someone like Salesforce or Google is better equiped than they are to manage user accounts, passwords, digital certificates, etc., the company could use OpenID Connect to essentially "outsource" that responsibility to an OpenID Connect Provider. When the company receives an id token in the context of an OpenID Connect flow, it knows that the provider has authenticated the end-user and established the user's identity.
OpenID Connect has repurposed the OAuth 2.0 flows so that the identity of an end-user can be established.
OIDC doesn't support Resource Owner Password Credentials Grant. Why? Some of my clients are secured devices which could safely maintain credentials... Those credentials could be used to get an access_token. Can I still use OpenID Connect?
It is not explicit in the specification but OpenID Connect supports all OAuth 2.0 flows since it is an extension of OAuth 2.0.
The spec talks about the flows that involve browser redirect as they are more common, more secure and less brittle given that resource owner credentials only supports username and password and is only in the OAuth 2 spec for backwards compatibility. In true SSO systems you'd want to abstract away from the method of authenticating the user at the OP/IDP. Involving a browser is a way to do that.
But your mileage may vary wrt. support in specific OP/AS software and client libraries.
FWIW: you should be looking to obtain an id_token rather than an access_token.
OpenID Connect performs authentication to log in the End-User or to
determine that the End-User is already logged in. OpenID Connect
returns the result of the Authentication performed by the Server to
the Client in a secure manner so that the Client can rely on it.
With implicit and authorization codes grant types flows, it is not possible to issue an ID token if the End-User is not logged in. In this case, the authorization server can confirm to the relying party that End-User is logged in.
But with the resource owner grant type flow, the authorization server cannot confirm the End-User is logged in. You can issue an access token even if the End-User is not logged in.
Yes. I also was finding answer for same question sometimes back. According to the OpenId Connect specification, It is recommended to use authorization code and implicit grant types for OpenId Connect requests. But it is not mentioned that other grant types can not be used. Therefore you can use any other grant types for OpenId Connect authentication request. There is some mail from the openid connect group, which has been discussed on this. Please find it from here. If your OAuth2 Authorization server supports it, I guess that it is fine to use it. As i know, most of the Authorization servers support it, as an example from here
I have been using OAuth resource owner credential flow previously for authorization.
However I would now like to consider using openid connect in pace of this, for authentication and authorization, and was wondering if the resource owner credential flow is supported in openid connect.
Yes, OpenID Connect supports all OAuth 2.0 grant types including Resource Owner Password Credentials Grant and Client Credentials Grant.
As we know, Authorization Code Grant and Implicit Grant are typical 3-legged flows including interaction between a client, an authorization server and a user. While the Resource Owner Password Credential Grant and Client Credential Grant are 2-legged which means the client uses pre-authorized scopes so that no interaction with the user is necessary, removing the need to perform one of the legs in the typical flow.
Here is a reference: Configuring an OpenID Connect Provider to enable 2-legged OAuth requests
The answer is YES. It is not explicit in the specification but OpenID Connect supports all OAuth 2.0 flows since it is an extension of OAuth 2.0.
The spec talks about the flows that involve browser redirect as they are more common, more secure and less brittle given that resource owner credentials only supports username and password and is only in the OAuth 2 spec for backwards compatibility.
In true SSO systems you'd want to abstract away from the method of authenticating the user at the OP/IDP. Involving a browser is a way to do that. In the Resource Owner Password Credentials flow the client "sees" the username/password of the Resource Owner unlike the other flows, which defeats the primary purpose of a federated SSO protocol like OpenID Connect where authentication mechanisms and credentials should be independent from the client/app. For that reason you won't see much use of ROPC in OpenID Connect, with an exception perhaps in intra-enterprise use cases.
But your mileage may vary wrt. support in specific OP/AS software and client libraries.
Yes. I also was finding answer for same question sometimes back. According to the OpenId Connect specification, It is recommended to use authorization code and implicit grant types for OpenId Connect requests. But it is not mentioned that other grant types can not be used. Therefore you can use any other grant types for OpenId Connect authentication request. There is some mail from the openid connect group, which has been discussed on this. Please find it from here. If your OAuth2 Authorization server supports it, I guess that it is fine to use it. As i know, most of the Authorization servers support it, as an example from here