A number of useful stored procedures related to users and roles within databases.
EXEC sp_HelpSrvRoleMember
EXEC sp_HelpLogins
EXEC sp_HelpUser
EXEC sp_HelProtect
EXEC sp_HelpRoleMember
Create a login (QuickRef).
CREATE LOGIN [(DOMAIN\)User] (FROM WINDOWS) WITH (PASSWORD = 'A34esdjdawki^tW4', ) DEFAULT_DATABASE = [DatabaseName]
Azure Database SPN
CREATE USER [SPN Identifier] FROM EXTERNAL PROVIDER
EXEC sp_addrolemember 'db_owner', [SPN Identifier]