docs: update docs for new enterprise default cfg

Add documentation about the new enterprise/registry settings.

Author: mjcheetham

README.md

@@ -189,6 +189,7 @@ See detailed information [here](https://aka.ms/gcmcore-httpproxy).
 - [Command-line usage](docs/usage.md)
 - [Configuration options](docs/configuration.md)
 - [Environment variables](docs/environment.md)
+- [Enterprise configuration](docs/enterprise-config.md)
 - [Network and HTTP configuration](docs/netconfig.md)
 - [Architectural overview](docs/architecture.md)
 - [Host provider specification](docs/hostprovider.md)

docs/configuration.md

@@ -8,7 +8,7 @@ Global configuration settings override system configuration settings, and local
 GCM Core honors several levels of settings, in addition to the standard local \> global \> system tiering Git uses.
 URL-specific settings or overrides can be applied to any value in the `credential` namespace with the syntax below.
 
-Additionally, GCM Core respects several GCM-specific [environment variables](environment.md) **which take precedence over configuration options.**
+Additionally, GCM Core respects several GCM-specific [environment variables](environment.md) **which take precedence over configuration options**. System administrators may also configure [default values](enterprise-config.md) for many settings used by GCM Core.
 
 GCM Core will only be used by Git if it is installed and configured. Use `git config --global credential.helper manager-core` to assign GCM Core as your credential helper. Use `git config credential.helper` to see the current configuration.
 

docs/enterprise-config.md

@@ -0,0 +1,57 @@
+# Enterprise configuration defaults
+
+Git Credential Manager Core (GCM Core) can be configured using multiple
+different mechanisms. In order of preference, those mechanisms are:
+
+1. [Environment variables](environment.md)
+2. [Standard Git configuration files](configuration.md)
+   1. Repository/local configuration (`.git/config`)
+   2. User/global configuration (`$HOME/.gitconfig` or `%HOME%\.gitconfig`)
+   3. Installation/system configuration (`etc/gitconfig`)
+3. Operating system specific configuration store
+
+This model largely matches what Git itself supports, namely environment
+variables that take precedence over Git configuration files.
+
+The addition of the operating system specific configuration store enables system
+administrators to configure defaults for many settings that may be required in
+an enterprise or corporate setting.
+
+---
+
+**Important:** We believe the user should _always_ be at liberty to configure
+Git and GCM exactly as they wish. By prefering environment variables and Git
+configuration files over OS store values, these only act as _default values_
+that can always be overriden by the user in the usual ways.
+
+---
+
+## Windows
+
+Default setting values come from the Windows Registry, specifically the
+`HKEY_LOCAL_MACHINE` hive under the following key:
+
+```text
+SOFTWARE\GitCredentialManager\Configuration
+```
+
+By using the Windows Registry system administrators can use Group Policy to
+easily set defaults for GCM Core's settings.
+
+The names and possible values of all settings under this key are the same as
+those of the [Git configuration](configuration.md) settings.
+
+The type of each registry key can be either `REG_SZ` (string) or `REG_DWORD`
+(integer).
+
+**Note:** GCM Core is a 32-bit executable on Windows. When running on a 64-bit
+installation of Windows registry access is transparently redirected to the
+`WOW6432Node`. This means the actual registry key on 64-bit Windows is:
+
+```text
+HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\GitCredentialManager\Configuration
+```
+
+## macOS/Linux
+
+Default configuration setting stores has not been implemented.

docs/environment.md

@@ -2,7 +2,7 @@
 
 [Git Credential Manager Core](usage.md) works out of the box for most users. Configuration options are available to customize or tweak behavior.
 
-Git Credential Manager Core (GCM Core) can be configured using environment variables. **Environment variables take precedence over [configuration](configuration.md) options.**
+Git Credential Manager Core (GCM Core) can be configured using environment variables. **Environment variables take precedence over [configuration](configuration.md) options**. System administrators may also configure [default values](enterprise-config.md) for many settings used by GCM Core.
 
 For the complete list of environment variables GCM Core understands, see the list below.