{doc} Add security guidance for az cmd execution

doc/cli_subprocess_guidelines.md

@@ -67,12 +67,66 @@ return output.stdout
 All various kinds of `subprocess` Popen calling use cases can be easily adjusted into `run_cmd` with security risks processed and eliminated in this centralized function.
 
 #### Notes
-Besides that, users might need to know some parts of the accessibility in both `run_cmd` and `subprocess`
+Besides that, developers might need to know some parts of the accessibility in both `run_cmd` and `subprocess`
 1. when calling shell built-in cmds, like `dir` or `echo`, using `shell=True` **in windows platform**, `subprocess` implicitly uses `cmd.exe`, while `run_cmd` asks developers to provide the `cmd.exe` as executable file specifically in the arg list's first item, like `["cmd.exe", "/c", "echo", "abc"]`
 2. if developers want to find an easy way to split their current cmd string into list, **for unix-like platforms**, developers can apply [`shlex.split`](https://docs.python.org/3/library/shlex.html#shlex.split) for quick access. But a prepared cmd statement is still more recommended (for more info about prepared cmd statement, please read below sections). 
 3. if developers want to locate the target command's executable file, a tool developers can use is `shutil.which` that gives the full executable file path in system, like `shutil.which(git)` returns the full `git.exe` path in windows platform `C:\\Program Files\\Git\\cmd\\git.EXE`. 
-4. if the target cmd is `az`-related, like `az group show --name xxxx`, please use internal function call `cli.invoke(["az", "group", "show", "--name", "xxx"])` from a newly created CLI context to get the target information.
+4. if the target cmd is `az`-related, like `az group show --name xxxx`, please see the following "`az`-related cmd execution" section.
 
+### `az`-related command execution
+
+If the target cmd is `az`-related, like `az group show --name xxxx`, instead of using `subprocess`, CLI recommends using internal function call to get the target information, as the following three options (if applicable):
+
+1. SDK operation. If target cmd is an operation from SDK, developers can apply corresponding method from SDK directly. For example:
+```python
+# code before:
+cmd = "az group show --name {}".format(resource_group_name)
+import json
+import subprocess
+output = subprocess.run(cmd, shell=True, check=False, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+resourceGroup = json.loads(output.stdout)
+location = resourceGroup['location']
+
+# code after:
+from azure.cli.core.commands.client_factory import get_mgmt_service_client
+from azure.cli.core.profiles import ResourceType
+resource_client = get_mgmt_service_client(cmd.cli_ctx, ResourceType.MGMT_RESOURCE_RESOURCES)
+location = resource_client.resource_groups.get(resource_group_name).location
+```
+
+2. Atomic cmd from codegen. If this cmd has been migrated through codegenV2, developers can call its atomic cmd. For example:
+```python
+# code before:
+cmd = "az monitor autoscale show --name {} --resource-group {}".format(autoscale_name, resource_group_name)
+import json
+import subprocess
+output = subprocess.run(cmd, shell=True, check=False, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+autoscale_settings = json.loads(output.stdout)
+
+# code after:
+from .aaz.latest.monitor.autoscale import Show as AutoScaleShow
+autoscale_settings = AutoScaleShow(cli_ctx=instance.cli_ctx)(command_args={
+    "resource_group": resource_group_name, 
+    "autoscale_name": autoscale_name
+})
+```
+
+3. if neither of the two methods above is applicable, developers can apply the central function `run_az_cmd` CLI provided to execute `az`-related cmds. For example:
+```python
+# code before:
+cmd = "az group show --name {}".format(resource_group_name)
+import json
+import subprocess
+output = subprocess.run(cmd, shell=True, check=False, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+resourceGroup = json.loads(output.stdout)
+location = resourceGroup['location']
+
+# code after:
+cmd = ["az", "group", "show", "--name", resource_group_name]
+from azure.cli.core.util import run_az_cmd
+resourceGroup = run_az_cmd(cmd).result
+location = resourceGroup['location']
+```
 
 ### Best practices in subprocess use cases
 
@@ -109,4 +163,4 @@ When using subprocess module, avoid `shell=True` argument when it comes with cmd
 
 
 ## Summary
-Ensuring the safety of Azure CLI from command injection under subprocess calling requires an in-depth understanding of these vulnerabilities and also proactive measures to counteract potential exploits. CLI developers should apply the security practices before using builtin `subprocess`, and it's recommended to use the centralized function `run_cmd` CLI provided, to safeguard CLI modules from command injection attack and for future more accessible security enforcements.
+Ensuring the safety of Azure CLI from command injection under subprocess calling requires an in-depth understanding of these vulnerabilities and also proactive measures to counteract potential exploits. CLI developers should apply the security practices before using builtin `subprocess`, and it's recommended to use the centralized function `run_cmd` CLI provided (or the applicable three methods for `az`-related cmds) , to safeguard CLI modules from command injection attack and for future more accessible security enforcements.