PowerShell Core Policy

1-Draft/RFCXXXX-Policy.md

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+---
+RFC:  RFCnnnn
+Author:  travisez13
+Status:  Draft
+SupercededBy:  N/A
+Version: 0.1
+Area: Engine
+Comments Due: 6/30/2019
+---
+
+# `PowerShell Core` Policy
+
+## Motivation
+
+Consumers, developers, and enterprise system administrators should be able to flexibly and reliably configure PowerShell 7.
+
+## Acknowledgement
+
+I based this off of @iSazonov 's RFC, for just a slightly different purpose.
+[PR #111](https://github.com/PowerShell/PowerShell-RFC/pull/111)
+
+## Goals
+
+1. Specify how PowerShell 7 will deal with having both Windows PowerShell and PowerShell Core Group Policy.
+    - This is covered in [Policy settings Setting Fall-Back](#policy-settings-setting-fall-back).
+1. Define how the `pwsh -settingsfile` switch should behave.
+    - This is covered in  [Parameter `-settingsfile`](#Parameter--settingsfile)
+
+## Definitions
+
+- **Computer-Wide settings/policy**  - setting or policy applied to an operating system environment (OSE), affecting all users of the OSE.
+- **User settings/policy** - setting or policy applied to a specific user of an OSE, and not applied to the OSE as a whole.
+
+## Specification
+
+`PowerShell 7` should be configured using the following schemes:
+
+- On Windows - Group Policy Objects (GPO), and settings files.
+- On Unix - settings files.
+
+The settings files have `JSON` format.
+
+**Warning** The settings files differ from `PowerShell 7` _profile_ files, which are PowerShell scripts run at startup.
+
+Configuration schemes allow to customize `PowerShell 7` in the most flexible way:
+
+- Enterprise system administrators can use GPO,
+    GPP and computer-wide settings files to apply approved configuration settings and mandatory security settings in a centralized manner.
+    Most settings can be applied either to the user or computer-wide.
+    We will cover the precedence of these in [Registry keys and settings](#registry-keys-and-settings).
+- Developers and consumers can use user, or computer-wide level setting files.
+
+### Configuration defaults
+
+PowerShell 7 has hard-coded defaults for all configuration policies and settings.
+
+The default values must be `secure-by-default`.
+
+For release versions hard-coded defaults must be the same as ones in pre-installed configuration files. For preview versions they may vary (ex., enable experimental features and so on).
+
+Computer-wide configuration includes security sensitive setting,
+and failing to read those setting, for example if the file is locked or corrupted, could result in an insecure system.
+So, if during startup, PowerShell 7 cannot read files read from the Computer-Wide scope,
+it fails to startup.
+
+If during startup PowerShell 7 cannot read user configuration files it uses _hardcoded_ defaults.
+
+PowerShell 7 does not update configuration values from modified configuration files during a given session after the configuration has been loaded.
+
+### Settings locations
+
+`PowerShell 7` settings are grouped into `Policy settings` and `Regular settings`.
+Regular settings are normal configuration settings.
+Regular settings can be treated as default and recommended values.
+Policy settings have a higher precedence than regular settings.
+See [Precedence for Policy settings in descending order](#precedence-for-policy-settings-in-descending-order).
+Policy settings are used by administrators to centrally manage PowerShell.
+
+| Location     | Policy settings                                           | Regular settings                                           |
+|--------------|-----------------------------------------------------------|------------------------------------------------------------|
+| File section | "PowerShell": { "PolicySettings": {...} }                 | "PowerShell": { "RegularSettings": {...} }                 |
+| Registry key | Software\Policies\PowerShellCore                          | Software\PowerShellCore                                    |
+
+### Policy settings Setting Fall-Back
+
+#### Motivation - Policy Setting Fall-Back
+
+This is to allow fall-back to Windows PowerShell policies.
+
+#### Implementation
+
+For Policy Settings,
+each policy should have a `Use Windows PowerShell Policy` which will indicate that the policy should the read from
+`SOFTWARE\Policies\Microsoft\Windows\PowerShell` instead of `Software\Policies\PowerShellCore`.
+The default in Group Policy is to have no policy, so it would not fall back to Windows PowerShell Policy, or apply PowerShell 7 policy.
+
+### Precedence of applying settings
+
+Because a configuration setting can be in several schemes, the setting wins according to the priority of its scheme.
+
+#### Precedence for Policy settings in descending order
+
+| Scheme                      | Windows                                              | Unix                                                 |
+|-----------------------------|------------------------------------------------------|------------------------------------------------------|
+| GPO -> Computer Policy      | HKLM\Software\Policies\PowerShellCore                | See [Moving configuration out of PSHome][moving]     |
+| GPO -> User Policy          | HKCU\Software\Policies\PowerShellCore                | See [`Comment A`](#comment-a) below                  |
+| File -> Computer-Wide       | See [Moving configuration out of PSHome][moving]     | [Moving configuration out of PSHome][moving]         |
+| File -> Application-Startup | pwsh -settingsfile `somepath/powershell.config.json` | pwsh -settingsfile `somepath/powershell.config.json` |
+| File -> User-Wide           | %APPDATA%/powershell.config.json                     | %XDG_CONFIG_HOME%/powershell.config.json             |
+
+Defaults:
+
+`%APPDATA%` - `C:\Users\useraccount\AppData\Roaming`
+
+`%XDG_CONFIG_HOME%` - `HOME/.config`
+
+#### Parameter `-settingsfile`
+
+With `-settingsfile` parameter users can assign custom settings from the config file and overwrite user-wide settings.
+
+##### More definitions
+
+- System Lock-down mode:
+  When Windows Defender Application Control or AppLocker force PowerShell into Constrained Language mode and
+  only trusted code runs in Full Language mode.
+  See [PowerShell Constrained Language Mode](https://devblogs.microsoft.com/powershell/powershell-constrained-language-mode/)
+
+##### Computer-wide and user policy settings
+
+Admin/root users can overwrite computer-wide and user policy settings using `-settingsfile`,
+only when not in System Lock-down mode.
+
+This will have performance impact on startup, but only when `-settingsfile` is specified.
+
+#### Priorities for Regular settings in descending order
+
+| Scheme                      | Windows                                              | Unix                                                 |
+|-----------------------------|------------------------------------------------------|------------------------------------------------------|
+| File -> Application-Startup | pwsh -settingsfile `somepath/powershell.config.json` | pwsh -settingsfile `somepath/powershell.config.json` |
+| File -> User-Wide           | %APPDATA%\powershell.config.json                     | ~/.config/powershell/powershell.config.json          |
+| File -> Computer-Wide       | %ProgramFiles%\PowerShell\powershell.config.json     | /opt/Microsoft/powershell/powershell.config.json     |
+| GPO -> User Config          | HKCU\Software\PowerShellCore                         | ~/.config/powershell/powershell.config.json|         |
+| GPO -> Computer Config      | HKLM\Software\PowerShellCore                         | /etc/powershell.config.json                          |
+
+### Configuration settings
+
+A set of configuration settings in GPO scheme and file scheme for policy settings and regular settings is the same. This allows to discover and configure settings in the simplest and fastest way.
+
+#### Registry keys and settings
+
+| Key                              | SubKey                      | Option                             | Type   | Precedence          |
+|----------------------------------|-----------------------------|------------------------------------|--------|---------------------|
+| Software\Policies\PowerShellCore | -                           | -                                  |        |                     |
+| Software\PowerShellCore          | -                           | -                                  |        |                     |
+|                                  |                             | ExecutionPolicy                    | String | Computer, Then User |
+|                                  | ConsoleSessionConfiguration | EnableConsoleSessionConfiguration  | DWORD  | User, then Computer |
+|                                  | ConsoleSessionConfiguration | ConsoleSessionConfigurationName    | String | User, then Computer |
+|                                  | ModuleLogging               | EnableModuleLogging                | DWORD  | Computer, Then User |
+|                                  | ModuleLogging               | ModuleNames                        | String | Computer, Then User |
+|                                  | ProtectedEventLogging       | EncryptionCertificate              | DWORD  | Computer Wide       |
+|                                  | ScriptBlockLogging          | EnableScriptBlockInvocationLogging | DWORD  | Computer, Then User |
+|                                  | ScriptBlockLogging          | EnableScriptBlockLogging           | DWORD  | Computer, Then User |
+|                                  | Transcription               | EnableTranscripting                | DWORD  | Computer, Then User |
+|                                  | Transcription               | EnableInvocationHeader             | DWORD  | Computer, Then User |
+|                                  | Transcription               | OutputDirectory                    | String | Computer, Then User |
+|                                  | UpdatableHelp               | DefaultSourcePath                  | String | Computer Wide       |
+
+I filed [#9632](https://github.com/PowerShell/PowerShell/issues/9632) on UpdatableHelp-DefaultSourcePath to make it allow User settings.
+
+#### JSON file settings format
+
+```json
+{
+  "PowerShell": {
+    "RegularSettings": {
+      "ConsoleSessionConfiguration": {
+        "EnableConsoleSessionConfiguration": true,
+        "ConsoleSessionConfigurationName": "name"
+      },
+      "ProtectedEventLogging": {
+        "EnableProtectedEventLogging": false,
+        "EncryptionCertificate": [
+          "Joe"
+        ]
+      },
+      "ScriptBlockLogging": {
+        "EnableScriptBlockInvocationLogging": true,
+        "EnableScriptBlockLogging": false
+      },
+      "ScriptExecution": {
+        "ExecutionPolicy": "RemoteSigned",
+        "PipelineMaxStackSizeMB": 10
+      },
+      "Transcription": {
+        "EnableTranscripting": true,
+        "EnableInvocationHeader": true,
+        "OutputDirectory": "c:\\tmp"
+      },
+      "UpdatableHelp": {
+        "DefaultSourcePath": "f:\\temp"
+      }
+    },
+
+    "PoliciesSettings": {
+      ...
+    }
+  }
+}
+```
+
+## Alternate Proposals and Considerations
+
+### Automatically resolve Windows PowerShell policy conflicts
+
+#### Motivation -  Automatically policy
+
+This is a description of the alternative to [Policy settings Setting Fall-Back](#policy-settings-setting-fall-back).
+The main purpose of describing the alternative is to describe why it should not be pursued.
+
+#### Description
+
+PowerShell could attempt to resolve policy conflicts between PowerShell 7 policy and Windows PowerShell policy.
+This would make the `Precedence for Policy settings` not just a simple list but a complex set of rules that would not be easily understood.  See [this conversation](https://github.com/PowerShell/PowerShell/issues/9309?#issuecomment-480643922).
+
+### Allowing environment variable in the JSON
+
+A new RFC should be drafted about how to allow environment variables in the values in the JSON.
+This would allow consistent files across platforms.
+
+### Moving configuration out of PSHome
+
+Per issues [9278](https://github.com/PowerShell/PowerShell/issues/9278) we need to move configuration out of PSHome,
+follow that issue for issues related to new locations of files.
+
+[moving]:#moving-configuration-out-of-pshome