Feature: AWS Cognito support (#1097)

* add Cognito support

* fix unnecessary formatting

* more unnecessary formatting

* Update package.json

* Update awsCognito.ts

* update package-lock.json

* Update awsCognito.ts

* Update package-lock.json

* fix ts-lint error

---------

Co-authored-by: Huachao Mao <huachaomao@gmail.com>

README.md

@@ -23,6 +23,7 @@ REST Client allows you to send HTTP request and view the response in Visual Stud
     - Azure Active Directory
     - Microsoft Identity Platform
     - AWS Signature v4
+    - AWS Cognito
 * Environments and custom/system variables support
     - Use variables in any place of request(_URL_, _Headers_, _Body_)
     - Support __environment__, __file__, __request__ and __prompt__ custom variables
@@ -381,6 +382,19 @@ GET https://httpbin.org/aws-auth HTTP/1.1
 Authorization: AWS <accessId> <accessKey> [token:<sessionToken>] [region:<regionName>] [service:<serviceName>]
 ```
 
+### AWS Cognito
+To authenticate via AWS Cognito, you need to set the Authorization header schema to `COGNITO` and provide your AWS credentials separated by spaces:
+- `<Username>`: AWS Username for target user
+- `<Password>`: AWS Password for target user
+- `<Region>`: AWS Region for Cognito pool
+- `<UserPoolId>`: AWS Cognito User Pool ID
+- `<ClientId>`: AWS Cognito Client ID
+
+```http
+GET https://httpbin.org/aws-auth HTTP/1.1
+Authorization: COGNITO <Username> <Password> <Region> <UserPoolId> <ClientId>
+```
+
 ## Generate Code Snippet
 ![Generate Code Snippet](https://raw.githubusercontent.com/Huachao/vscode-restclient/master/images/code-snippet.gif)
 Once you’ve finalized your request in REST Client extension, you might want to make the same request from your source code. We allow you to generate snippets of code in various languages and libraries that will help you achieve this. Once you prepared a request as previously, use shortcut `Ctrl+Alt+C`(`Cmd+Alt+C` for macOS), or right-click in the editor and then select `Generate Code Snippet` in the menu, or press `F1` and then select/type `Rest Client: Generate Code Snippet`, it will pop up the language pick list, as well as library list. After you selected the code snippet language/library you want, the generated code snippet will be previewed in a separate panel of Visual Studio Code, you can click the `Copy Code Snippet` icon in the tab title to copy it to clipboard.