SQL Server 2019 Users and Security |SQL Server 2019: Security with Users, Schemas, and Roles

Permissions Hierarchy
SQL Server 2019 Users and Security |SQL Server 2019: Security with Users, Schemas, and Roles
The Database Engine manages a hierarchical collection of entities that can be secured with permissions. These entities are known as securable. The most prominent securables are servers and databases, but discrete permissions can be set at a much finer level. SQL Server regulates the actions of principals on securables by verifying that they have been granted appropriate permissions
Principals
Principals are entities that can request SQL Server resources. Like other components of the SQL Server authorization model, principals can be arranged in a hierarchy. A Windows Login is an example of an indivisible principal, and a Windows Group is an example of a principal that is a collection. Every principal has a security identifier (SID).
Principals Contd
Windows-level principals
Windows Domain Login
Windows Local Login
SQL Server-level principals
SQL Server Login
Server Role
Database-level principals
Database User
Database Role
Application Role
A Login in SQL Server 2019
A login is a security principal, or an entity that can be authenticated by a secure system.
Users need a login to connect to SQL Server.
You can create a login based on a Windows principal (such as a domain user or a Windows domain group) or you can create a login that isn't based on a Windows principal (such as an SQL Server login).
A Login in SQL Server 2019
As a security principal, permissions can be granted to logins.
The scope of a login is the whole Database Engine.
To connect to a specific database on the instance of SQL Server, a login must be mapped to a database user.
Permissions inside the database are granted and denied to the database user, not the login.
Security
SQL Server requires ALTER ANY LOGIN or ALTER LOGIN permission on the server.
SQL Database requires membership in the loginmanager role.
Server Roles
The Server Roles page lists all possible roles that can be assigned to the new login.
SQL Server provides server-level roles to help you manage the permissions on a server.
The permissions that are granted to the fixed server roles cannot be changed.
bulkadmin to run the BULK INSERT statement.
dbcreator to create, alter, drop, and restore any database.
diskadmin to manage disk files.
processadmin to terminate processes running in an instance of the Database Engine.
public All users, groups, and roles belong to the public server role by default.
securityadmin to manage logins and their properties.
serveradmin to change server-wide configuration options and shut down the server.
sysadmin to perform any activity in the Database Engine.
Permission to connect to database engine
When you work with this setting, you should think of the selected login as a principal that can be granted or denied permission on a securable.
Select Grant to grant CONNECT SQL permission to the login.
Select Deny to deny CONNECT SQL to the login.
A login that has been disabled continues to exist as a record. But if it tries to connect to SQL Server, the login won't be authenticated.
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