OAuth vs SSO: Which One Should I Use?

Currently, I am working on one project which provided me a lot of opportunities to learn about OAuth 2.0 and SAML and better understanding on which one to choose for SSO strategy.
I am choosing this topic because most of the people get confused between these two. While they have some similarities but they are very different too and to put it one line. I would say “OAuth is not Single Sign-On”

What is the difference between OAuth 2.0 and SSO?

OAuth (Open Authorization) is a standard for authorization of resources. It does not deal with authentication. It allows secure authorization in a simple and standard method from web, mobile and desktop applications.

If you try to log into Stack Overflow using Facebook, you’ll be redirected to Facebook’s website and will see something like the following:

Once authenticated with Facebook, it will ask for Stack Overflow’s permission to access your resources like your name, Email id, Profile picture and so on. This is an authorization request like what Stack Overflow can do and what cannot do?

SAML: Security Assertion Markup Language is an XML-based open standard data format for exchanging authentication and authorization data between parties, in particular, between an identity provider and a service provider. It is an umbrella standard that encompasses profiles, bindings and constructs to achieve Single Sign-On (SSO), Federation and Identity Management.

SSO is an authentication/authorization flow through which a user can log into multiple services using the same credentials.
For instance, at your company where we have various applications like leave application, lunch application, career application and so on and we can configure all these applications to one Active Directory for authentication. Another example can be Atlassian account where you once logged in can use their other applications like Bamboo, JIRA, Confluence and so on.

Both examples represent SSO.

One of the main benefits to using SSO is that your users have only a single account and password to remember which gets them into all of their services.

Conclusion: When Should I Use Which?

• If your use case requires a single account to log into many applications, then go with SSO like your internal company applications.
• If your use case involves providing access (temporarily or permanent) to resources (such as accounts, pictures, files etc.), then use OAuth.
• If your use case requires a centralized identity source, then use SSO.
• If your case requires to have accounts on many different services, and selectively grant access to various services, use OAuth