docs: adding document for servers' security

pages/docs/concepts/asyncapi-document/_section.md

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+---
+title: 'AsyncAPI Document'
+weight: 50
+---

pages/docs/concepts/asyncapi-document/server-security.md

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+---
+title: Server Security 
+weight: 200
+---
+
+Server security refers to the measures and practices implemented to protect servers from unauthorized access, data breaches, and other security threats. Server security involves implementing various security mechanisms to ensure the confidentiality, integrity, and availability of server resources.
+
+In the context of AsyncAPI, securing servers ensures secure exchange of messages between clients and servers. While also protecting sensitive data, preventing unauthorized access, and maintaining the overall security of the API or server.
+
+You can secure a server by using the `security` property where you define or declare which security schemes can be used with the server in context. Each `server` in the AsyncAPI document can have one or more security schemes declared. A security scheme defines a security requirement that must be satisfied to authorize an operation such as a API key or username and password. 
+
+Here is a example of adding security to your server:
+```yml
+asyncapi: '3.0.0'
+info:
+  title: My AsyncAPI
+  version: '1.0.0'
+servers:
+  production:
+    url: api.example.com
+    protocol: amqp
+    security:
+      - saslScram: []
+      - certs: []
+components:
+  securitySchemes:
+    saslScram:
+      type: scramSha256
+      description: Provide your username and password for SASL/SCRAM authentication
+    certs:
+      type: X509
+      description: Download the certificate files from service provider
+```
+
+Here is a illustration of securing servers: 
+```mermaid
+graph LR
+  A[asyncapi: '3.0.0'] --> B[info]
+  A --> C[servers]
+  A --> D[components]
+  D --> I
+  D --> J
+
+  B --> E[title, version]
+
+  C -->F[production]
+  F --> G[url, protocol, security]
+  G -->|Security Schemes| H[saslScram, certs]
+  I[type, description]
+  J[type, description]
+```
+
+Here are some of the security schemes that AsyncAPI supports:
+- User/Password
+  ```yml
+  type: userPassword
+  ```
+
+- API key (either as a user or as a password)
+```yml
+type: apiKey
+in: user
+```
+
+- X.509 certificate
+```yml
+type: X509
+```
+
+- End-to-end encryption (either symmetric or asymmetric)
+```yml
+type: symmetricEncryption
+```
+
+- HTTP authentication
+```yml
+type: http
+scheme: basic
+```
+
+- HTTP API key
+```yml
+type: httpApiKey
+name: api_key
+in: header
+```
+
+- JWT Bearer
+```yml
+type: http
+scheme: bearer
+bearerFormat: JWT
+```
+
+- Implicit oauth2
+```yml
+type: oauth2
+flows:
+  implicit:
+    authorizationUrl: https://example.com/api/oauth/dialog
+    availableScopes:
+      write:pets: modify pets in your account
+      read:pets: read your pets
+scopes:
+  - 'write:pets'
+```
+
+- SASL (Simple Authentication and Security Layer) as defined in RFC4422
+```yml
+type: scramSha512
+```
+
+Although, the `security` property is not mandatory to be implemented, it is a good practise to always secure your server(s) in production. Similarly, having multiple security schemes declared does not necessarily mean that the server is more secure, it really depends on other factors such as the protocol used, use case, business perspective and more.