[Modify/Add] Add more doc. and some typo fix

sections/advanced_identity.md

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+# Advanced Identity
+
+- [Advanced Identity](#advanced-identity)
+  - [AWS STS (Security Token Service)](#aws-sts-security-token-service)
+  - [Amazon Cognito](#amazon-cognito)
+  - [Microsoft Active Directory (AD)](#microsoft-active-directory-ad)
+    - [AWS Directory Services](#aws-directory-services)
+  - [AWS IAM Identity Center](#aws-iam-identity-center)
+  - [Summary](#summary)
+
+## AWS STS (Security Token Service)
+
+- Provides temporary, limited-privilege credentials to access AWS resources
+- Credentials have a configurable expiration period
+- Use cases:
+  - Identity federation: manage user identities in external systems, providing STS tokens for AWS resource access
+  - IAM Roles for cross-account or same-account access
+  - IAM Roles for EC2 instances: temporary credentials for EC2 to access AWS resources
+
+## Amazon Cognito
+
+- Manages identity for web and mobile application users (potentially millions)
+- Instead of creating IAM users, create users in Cognito
+
+## Microsoft Active Directory (AD)
+
+- Available on any Windows Server with AD Domain Services
+- Database of objects: user accounts, computers, printers, file shares, security groups
+- Centralized security management, create accounts, assign permissions
+
+### AWS Directory Services
+
+- **AWS Managed Microsoft AD**
+  - Create and manage your own AD in AWS, supports MFA
+  - Establish trust connections with on-premise AD
+- **AD Connector**
+  - Directory gateway (proxy) to redirect to on-premise AD, supports MFA
+  - Users are managed on the on-premise AD
+- **Simple AD**
+  - AD-compatible managed directory on AWS
+  - Cannot be joined with on-premise AD
+
+## AWS IAM Identity Center
+
+- Single sign-on (SSO) for:
+  - AWS accounts in AWS Organizations
+  - Business cloud applications (e.g., Salesforce, Box, Microsoft 365)
+  - SAML 2.0-enabled applications
+  - EC2 Windows instances
+- Identity providers:
+  - Built-in identity store in IAM Identity Center
+
+## Summary
+
+- **IAM**: Identity and Access Management within your AWS account for trusted users within your company
+- **Organizations**: Manage multiple AWS accounts
+- **Security Token Service (STS)**: Temporary, limited-privilege credentials for AWS resource access
+- **Cognito**: Create a user database for mobile and web applications
+- **Directory Services**: Integrate Microsoft Active Directory in AWS
+- **IAM Identity Center**: Single login for multiple AWS accounts and applications