OAuth vs SAML vs Kerberos

They are all ways to help authenticate and authorize users/services to another service through an identity provider. They use different strategies and have some differences between them.

OAuth:

Parties are: Client, Service Provider, and Authorization Provider
Main task: It gives a service provider access to some resource through the Authorization Provider requiring Client’s consent
OAuth allows to give scopes to these service providers to have certain access
OAuth returns an Access Token to be used by the service provider
OAuth can have an identity layer and it’s named OpenId Connect or OIDC, it returns also an Id Token which is used to identify the user
JSON-Based and uses JWTs
More modern and used by newer apps
Doesn’t require prior introduction between the Authorization Provider and Service Provider making it easy to setup

SAML:

Used mainly for Authentication but can have an authorization layer
Parties are: Client, Service Provider and Identity provider
Main task: it gives access to a client to a service provider through the identity provider
Very similar to OIDC
XML based and used by older applications and government software

Kerberos

Used mainly for Authentication & Authorization among a bunch of services with asymmetric keys (no public key) and avoid sharing keys between these many services
Parties: many services and a Key Distribution Center which includes two servers Authentication server and Ticket Granting server
Main Task: Gives access and keys to a service to communicate with another service using a session key