TheSecurity with Spring tutorials focus, as you’d expect, on Spring Security.
Get started with the Registration series if you’re interested in building a registration flow, and understanding some of the frameworks basics.
Then, explore authentication and other Spring Security internals in-depth.
Finally, have a look at some of the more advanced topics, such as the OAuth support.

Registration with Spring Security
Spring Security Registration Series(Series)Build a registration flow with Spring Security

Authentication with Spring Security
Spring Security Form Login(popular)
Spring Security Basic Authentication(popular)
Spring Security Authentication Provider(popular)
How to Manually Authenticate User with Spring Security
Spring Security Custom AuthenticationFailureHandler
Spring Security Login Page with React
Spring Security: Upgrading the Deprecated WebSecurityConfigurerAdapter(popular)
Securing Spring Boot API With API Key and Secret(popular)
Securing Spring Boot Applications With SSL Bundles(popular)
Two Factor Auth with Spring Security(popular)
Authenticating Users with AzureAD in Spring Boot(popular)

Authorization with Spring Security

Core Spring Security
Spring Boot Security Auto-Configuration(popular)
Retrieve User Information in Spring Security(popular)
Spring Security - permitAll() and web.ignoring()
Control the Session with Spring Security(popular)
A Custom Filter in the Spring Security Filter Chain(popular)
Handle Spring Security Exceptions With @ExceptionHandler(popular)
Enable Logging for Spring Security
SAML with Spring Boot and Spring Security(popular)
Disable Security for a Profile in Spring Boot
A Guide to CSRF Protection in Spring Security(popular)
Prevent Cross-Site Scripting (XSS) in a Spring Application

OAuth2 with Spring Security
Spring Security OAuth 2 Series(popular)(Series)Learn about OAuth2 with Spring Security, using both the Spring Security 5 stack, as well as the Spring Security OAuth legacy stack.

Other Spring Tutorials
REST with Spring Series(popular)(Series)How to build REST Services with Spring
Spring Persistence Series(popular)(Series)How to Build the Persistence Layer of an application with Spring and Hibernate, JPA, Spring Data, etc
Spring Exceptions Series(Series)Common Exceptions in Spring with examples – why they occur and how to solve them quickly