You are who you are. YOur ID as an individual account or session. Who
The access to make the request and access the data it wants. Boarding pass. What security clearance.
auth code flow with proof key PKCE
implicit flow ** not affected by security issues of doing an native implicit grant
Hybryd Flow ** no 3rd party clients
Authorization standard adopted by a wide range of websites. Like a valet key, allows for a site to temporarily authorize data from an otherwise separate system. Gives a site tempiorary access to park and retrieve your car.
'The first website connects to the second website on behalf of the user, using OAuth, providing the user’s verified identity. The second site generates a one-time token and a one-time secret unique to the transaction and parties involved. The first site gives this token and secret to the initiating user’s client software. The client’s software presents the request token and secret to their authorization provider (which may or may not be the second site). If not already authenticated to the authorization provider, the client may be asked to authenticate. After authentication, the client is asked to approve the authorization transaction to the second website. The user approves (or their software silently approves) a particular transaction type at the first website. The user is given an approved access token (notice it’s no longer a request token). The user gives the approved access token to the first website. The first website gives the access token to the second website as proof of authentication on behalf of the user. The second website lets the first website access their site on behalf of the user. The user sees a successfully completed transaction occurring. OAuth is not the first authentication/authorization system to work this way on behalf of the end-user. In fact, many authentication systems, notably Kerberos, work similarly. What is special about OAuth is its ability to work across the web and its wide adoption. It succeeded with adoption rates where previous attempts failed (for various reasons).' [Source](https://www.csoonline.com/article/3216404/what-is-oauth-how-the-open-authorization-framework-works.html)
not used as much, but open ID has become the authorization layer common with OAuth. “OpenID is for humans logging into machines, OAuth is for machines logging into machines on behalf of humans.”
The Security Assertion Markup Language is a little older and more secure. More common for enterprise. Salesforce deals in this.