This is a reproduction of an AWS Support response. I use AWS support in my own personal account for ~29USD a month. They’re awesome and I did get permission to reproduce their response to my SSO versus Oauth2 questions below:
From your correspondence you mentioned that you would like to create a Web Application that authenticates against https://webc.awsapps.com/start . You state that you are not sure of how it fits with Cognito or OAuth2. You shared the link https://www.reddit.com/r/aws/comments/h01n75/single_sign_on_start_questions/ftqpnpi to provide a context to your query. You are also seeking clarification as to why Amazon Cognito is not supported as in this link https://docs.aws.amazon.com/singlesignon/latest/userguide/supported-idps.html
There are several issues that are parked into your query. To address the issues you have raised, I will first define Single Sign-On as a concept followed brief definitions of OAuth and SAML. I will then give a brief overview of AWS SSO and AWS Cognito and lastly give a recommendation on the application that you would like to create.
What is SSO?
Single sign-on (SSO) provides the procedures needed to guarantee that a user, after performing a single authentication, can access multiple systems. For this to take place, the SSO system must communicate with every external app to tell them that the user is signed in — which is where SAML comes into play.
SAML 2.0 is a standard for exchanging authentication and authorization identities between security domains. SAML 2.0 uses security tokens containing assertions to pass information about a principal (usually an end user) between a SAML authority, named an Identity Provider, and a SAML consumer, named a Service Provider. SAML 2.0 enables web-based, cross-domain SSO, which helps reduce the administrative overhead of distributing multiple authentication tokens to the user.
SAML 2.0 Use Cases
- If your use case involves SSO (when at least one actor or partner is an enterprise)
- If your use case involves providing access to a partner or customer application to your portal
- If your use case requires a centralized identity source
In the traditional client-server authentication model, the client requests an access-restricted resource (protected resource) on the server by authenticating with the server using the resource owner’s credentials. In order to provide third-party applications access to restricted resources, the resource owner shares its credentials with the third party. This creates several problems and limitations:
- Third-party applications are required to store the resource owner’s credentials for future use, typically a password in clear-text.
- Servers are required to support password authentication, despite the security weaknesses inherent in passwords.
- Third-party applications gain overly broad access to the resource owner’s protected resources, leaving resource owners without any ability to restrict duration or access to a limited subset of resources.
- Resource owners cannot revoke access to an individual third party without revoking access to all third parties, and must do so by changing the third party’s password
- Compromise of any third-party application results in compromise of the end-user’s password and all of the data protected by that password
The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. In OAuth, the client requests access to resources controlled by the resource owner and hosted by the resource server, and is issued a different set of credentials than those of the resource owner. Instead of using the resource owner’s credentials to access protected resources, the client obtains an access token – a string denoting a specific scope, lifetime, and other access attributes. Access tokens are issued to third-party clients by an authorization server with the approval of the resource owner. The client uses the access token to access the protected resources hosted by the resource server.
OAuth 2.0 Use Cases
- If your use case involves providing access(temporarily or permanent) to resources (such as accounts, pictures, files etc.)
- If your use case involves mobile devices– then use OAuth (with some form of bearer tokens).
SAML with OAuth
Since OAuth is only an authoritarian framework, its possible to;
- Use SAML for authentication.
- Use SAML token/assertion as the OAuth bearer token in the HTTP bearer header to access protected resources.
What is AWS SSO?
AWS Single Sign-On is a cloud-based single sign-on (SSO) service that makes it easy to centrally manage SSO access to all of your AWS accounts and cloud applications. Specifically, it helps you manage SSO access and user permissions across all your AWS accounts in AWS Organizations. AWS SSO also helps you manage access and permissions to commonly used third-party software as a service (SaaS) applications, AWS SSO-integrated applications as well as custom applications that support Security Assertion Markup Language (SAML) 2.0. AWS SSO includes a user portal where your end-users can find and access all their assigned AWS accounts, cloud applications, and custom applications in one place.
For an overview of Amazon SSO showing the key features of the, the usage scenarios, authentication process please see this slide
What is Amazon Cognito?
Amazon Cognito provides authentication, authorization, and user management for your web and mobile apps. Your users can sign in directly with a user name and password, or through a third party such as Facebook, Amazon, Google or Apple. The two main components of Amazon Cognito are user pools and identity pools. You can use identity pools and user pools separately or together. Amazon Cognito user pools also support the OAuth 2.0 authorization framework for authenticating users.
For an overview of Amazon Cognito showing the key features of the, the usage scenarios, authentication process please see this Cognito slide.
You asked about the AWS SSO not supporting Amazon Cognito as an Identity provider. This is because AWS Cognito is not a SAML 2.0 Identity provider.
Your other request was on how create an app that users will access by authenticating through https://webc.awsapps.com/start . To use this URL means that you will be using AWS SSO. AWS SSO will be acting as an Identity provider while your custom application will acting as a service provider.
If this is your use case, to achieve this you will first need to create your SAML 2.0 compliant application in your language of choice. AWS does not have any guide for creating SAML 2.0 applications. After some research I found Passport-SAML which is an authentication provider for Passport-the Node.js authentication library. Please note that AWS does not endorse nor provide support for content on third party links and that you will use them at your own discretion.
After you have created the SAML 2.0 compliant application you can then follow the instructions on integration with AWS SSO.
If your use case is to create a Web application for users outside (authenticate by self registration,Facebook or Google) your organisation without need for interaction with AWS resources, I highly recommend that you use Amazon Cognito instead of AWS SSO. Amazon Cognito lets you add user sign-up, sign-in, and access control to your web and mobile apps quickly and easily. Amazon Cognito scales to millions of users and supports sign-in with social identity providers, such as Facebook, Google, and Amazon, and enterprise identity providers via SAML 2.0.
To integrate Amazon Cognito with your web or mobile app, use the SDKs and libraries that the AWS Amplify framework provides.
I hope this information answers your question and is helpful. Otherwise, please provide me with your specific use case in order for me to be able to help further.
-  Single sign-on https://en.wikipedia.org/wiki/Single_sign-on
-  SAML 2.0 https://en.wikipedia.org/wiki/SAML_2.0
-  The OAuth 2.0 Authorization Protocol https://tools.ietf.org/id/draft-ietf-oauth-v2-12.xml
-  OAuth and Federation Overview https://docs.amplify.aws/lib/auth/social/q/platform/js
-  Introducing AWS Single Sign-On https://aws.amazon.com/blogs/security/introducing-aws-single-sign-on/
-  Deep Dive on AWS Single Sign-On - AWS Online Tech Talks https://www.slideshare.net/AmazonWebServices/deep-dive-on-aws-single-signon-aws-online-tech-talks
-  Understanding Amazon Cognito user pool OAuth 2.0 grants https://aws.amazon.com/blogs/mobile/understanding-amazon-cognito-user-pool-oauth-2-0-grants/
-  Amazon Cognito Deep Dive https://www.slideshare.net/AmazonWebServices/amazon-cognito-deep-dive
-  Passport-SAML http://www.passportjs.org/packages/passport-saml/
-  Custom SAML 2.0 Applications https://docs.aws.amazon.com/singlesignon/latest/userguide/samlapps.html
-  Integrating Amazon Cognito With Web and Mobile Apps https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-integrate-apps.html