This commit introduces the ability to use system environment variables
within the settings files (e.g., `settings.json`). Users can now
reference environment variables using the `${VAR_NAME}` syntax.
This enhancement improves security and flexibility, particularly
for configurations like MCP server settings, which often require
sensitive tokens.
Previously, to configure an MCP server, a token might be directly
embedded:
```json
"mcpServers": {
"github": {
"env": {
"GITHUB_PERSONAL_ACCESS_TOKEN": "pat_abc123"
}
// ...
}
}
```
With this change, the same configuration can securely reference an
environment variable:
```json
"mcpServers": {
"github": {
"env": {
"GITHUB_PERSONAL_ACCESS_TOKEN": "${GITHUB_PERSONAL_ACCESS_TOKEN}"
}
// ...
}
}
```
This allows users to avoid storing secrets directly in configuration files.
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