feat: add plugin schema

docs/plugin-descriptor-schema.md

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+# CRS Plugin Descriptor Schema
+
+## Overview
+
+The plugin descriptor schema defines a `plugin.yaml` file that lives in the root of each CRS plugin repository. It provides machine-readable metadata about the plugin, its configuration variables, and compatibility requirements.
+
+The plugin registry aggregates these descriptors to generate the registry table, and downstream tooling (such as a CRS configurator) can parse them to build preconfigured CRS deployments based on plugin selection.
+
+## Goals
+
+- Allow each plugin repository to be the single source of truth for its own metadata.
+- Enable automated tooling to discover, validate, and configure plugins.
+- Replace manual registry table maintenance with generated output.
+- Provide enough information for a configurator to present a UI for plugin selection and variable tuning.
+
+## Schema Structure
+
+The schema is defined as [JSON Schema (2020-12)](https://json-schema.org/draft/2020-12/json-schema-core) in [`plugin-schema.json`](../plugin-schema.json). A `plugin.yaml` file has the following top-level sections:
+
+### `schema_version`
+
+**Required.** Integer, currently fixed at `1`.
+
+Allows future evolution of the schema without breaking existing parsers. Tooling should check this field and handle unknown versions gracefully.
+
+### `plugin`
+
+**Required.** Plugin identity and metadata.
+
+| Field              | Required | Description |
+|--------------------|----------|-------------|
+| `name`             | yes      | Plugin name following the CRS convention: `<name>-plugin`. Validated by regex. |
+| `description`      | yes      | One-line summary of the plugin's purpose. |
+| `long_description` | no       | Multi-line extended description for documentation and UI display. |
+| `type`             | yes      | `official` (coreruleset-maintained) or `3rd-party`. |
+| `category`         | no       | Functional category: `rule-exclusion`, `detection`, `protection`, `utility`, `logging`, or `performance`. |
+| `status`           | yes      | Maturity level: `tested`, `being-tested`, `untested`, or `draft`. |
+| `license`          | yes      | SPDX license identifier (e.g., `Apache-2.0`, `GPL-2.0-only`). |
+| `authors`          | yes      | List of author objects with `name` (required), `email` and `url` (optional). |
+| `repository`       | yes      | URL of the plugin GitHub repository (only GitHub repositories are currently supported). |
+| `homepage`         | no       | URL to documentation or project site. |
+| `keywords`         | no       | Tags for discovery and categorization. |
+
+### `rule_id_range`
+
+**Required.** The registered rule ID block from the plugin registry.
+
+| Field   | Description |
+|---------|-------------|
+| `start` | First rule ID in the allocated range (integer, 9500000-9999999). |
+| `end`   | Last rule ID in the allocated range (integer, 9500000-9999999). |
+
+Plugins typically receive a 1,000-ID range. The schema validates that values fall within the CRS plugin namespace (9,500,000 - 9,999,999).
+
+### `compatibility`
+
+**Optional.** WAF engine and CRS version requirements.
+
+| Field         | Description |
+|---------------|-------------|
+| `crs_version` | Version constraint string (e.g., `>=4.0.0`). |
+| `engines`     | List of compatible WAF engines, one of: `modsecurity2`, `modsecurity3`, `coraza`, `all`. |
+
+When omitted, no compatibility constraints are assumed. Tooling should treat missing `engines` field as if `engines` were set tp `all`.
+
+### `dependencies`
+
+**Optional.** List of other CRS plugins this plugin depends on.
+
+Each entry has:
+| Field     | Required | Description |
+|-----------|----------|-------------|
+| `name`    | yes      | Name of the required plugin. |
+| `version` | no       | Version constraint for the dependency. |
+
+Most plugins have no dependencies. This field exists for plugins that build on top of other plugins.
+
+### `configuration`
+
+**Required.** The key section for automated tooling. Describes the config file and all user-tunable variables.
+
+| Field       | Description |
+|-------------|-------------|
+| `file`      | Path to the `-config.conf` file relative to the plugin root. |
+| `variables` | List of transaction variable definitions (see below). |
+
+#### Variable Definition
+
+Each entry in `variables` describes a single `tx.*` variable from the config file:
+
+| Field            | Required | Description |
+|------------------|----------|-------------|
+| `name`           | yes      | Full ModSecurity variable name (e.g., `tx.myplugin_enabled`). |
+| `type`           | yes      | Data type: `boolean`, `integer`, `string`, `list`, or `enum`. |
+| `default`        | no       | Default value if not set by the user. |
+| `description`    | yes      | Human-readable explanation of the variable. |
+| `required`       | no       | Whether the user must explicitly set this variable (default: `false`). |
+| `allowed_values` | no       | List of valid values when type is `enum`. |
+| `separator`      | no       | String used to separate multiple entries when type is `list`. |
+| `prefix`         | no       | String marking the beginning of a list entry when type is `list`. |
+| `suffix`         | no       | String marking the end of a list entry when type is `list`. |
+| `example`        | no       | Example value for documentation. |
+| `min`            | no       | Minimum value when type is `integer`. |
+| `max`            | no       | Maximum value when type is `integer`. |
+
+#### Variable Types
+
+The four types cover all patterns found across existing CRS plugins:
+
+- **`boolean`** — Enable/disable flags. Every plugin has at least `tx.<name>_enabled`. Values are integers: `0` (disabled) or `1` (enabled), following the ModSecurity convention for boolean flags.
+- **`integer`** — Numeric thresholds and limits (e.g., `tx.body-decompress-plugin_max_data_size_bytes`). Supports `min`/`max` constraints.
+- **`string`** — Freeform text values. The `example` field helps users understand the expected format.
+- **`list`** — Structured list of strings (e.g., `tx.google-oauth2-plugin_whitelisted_parameters`). The fields `separator`, `prefix`, `suffix` define the format. For example, the list `|a/ |b/ |c/` would be defined as follows:
+  - `separator`: `" "` (space character)
+  - `prefix`: `"|"`
+  - `suffix`: `"/"`
+- **`enum`** — Constrained choices (e.g., `tx.phpmyadmin-rule-exclusions-plugin_url_format` with values `v51`, `v52`). Must include `allowed_values`.
+
+## Design Decisions
+
+### Why YAML over JSON or TOML?
+
+YAML supports comments, multi-line strings, and is widely used in the CRS ecosystem (test files use FTW YAML format). Plugin authors already work with YAML for regression tests, so it is familiar.
+
+### Why `schema_version` as a top-level field?
+
+Embedding versioning in the schema itself allows parsers to detect incompatible changes before attempting to parse. This is simpler than relying on file naming or external version tracking.
+
+### Why typed variables with constraints?
+
+A configurator project needs to know more than just variable names and defaults. By declaring types, allowed values, and numeric bounds, tooling can:
+
+1. Render appropriate input widgets (toggle for boolean, slider for bounded integer, dropdown for enum).
+2. Validate user input before generating configuration.
+3. Generate documentation automatically.
+
+### Why is `configuration` required?
+
+Every CRS plugin has at least one configuration variable (`tx.<name>_enabled`). Making this section required ensures consistency and guarantees that tooling always has something to work with, even for minimal rule-exclusion plugins.
+
+### Why no `version` field?
+
+The plugin version is derived from GitHub release tags at query time. Embedding a version in `plugin.yaml` would inevitably drift because developers forget to bump it. Tooling should fetch the latest release tag from the repository URL instead. This keeps `plugin.yaml` as a static descriptor that rarely needs updating.
+
+### Why separate `rule_id_range` from `plugin`?
+
+The rule ID range is a registry-level concern (namespace coordination), not a plugin identity attribute. Keeping it separate makes it clear that this range is allocated by the registry and should not be changed unilaterally.
+
+### Category taxonomy
+
+The six categories cover the existing plugin landscape:
+
+| Category         | Examples |
+|------------------|----------|
+| `rule-exclusion` | wordpress, drupal, nextcloud, phpbb, cpanel |
+| `detection`      | fake-bot |
+| `protection`     | dos-protection |
+| `utility`        | template, body-decompress, auto-decoding |
+| `logging`        | database-logging, false-positive-report |
+| `performance`    | performance-plugin |
+
+New categories can be added to the schema's enum as the ecosystem grows.
+
+### Engine taxonomy
+
+The supported WAF engines are:
+
+| Engine           | Description |
+|------------------|-------------|
+| `modsecurity2`   | ModSecurity 2.x (Apache module) |
+| `modsecurity3`   | ModSecurity 3.x (connector-based, e.g. nginx) |
+| `coraza`         | Coraza WAF |
+| `all`            | Compatible with all supported engines |
+
+New engines can be added to the schema's enum as the ecosystem grows.
+
+## Configurator Integration
+
+The primary consumer of `plugin.yaml` files is a configurator tool that:
+
+1. **Fetches** `plugin.yaml` from each registered plugin repository.
+2. **Presents** available plugins grouped by category, with descriptions and compatibility info.
+3. **Collects** user choices: which plugins to enable and how to tune their variables.
+4. **Validates** input against variable constraints (type, min/max, allowed_values).
+5. **Resolves** dependencies between plugins.
+6. **Generates** a complete CRS configuration with all selected plugins and their tuned `tx.*` variables.
+
+## Rollout Plan
+
+1. Add `plugin.yaml` to `coreruleset/template-plugin` as the reference implementation.
+2. Get feedback from the CRS team and iterate on the schema.
+3. Once the schema is accepted, create PRs adding `plugin.yaml` to all registered plugins.
+4. Update the registry to validate incoming plugin registrations against the schema.
+5. Build the configurator project.

examples/body-decompress-plugin.yaml

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+# OWASP CRS Plugin Descriptor
+# https://github.com/coreruleset/plugin-registry
+
+schema_version: 1
+
+plugin:
+  name: "body-decompress-plugin"
+  description: "On-the-fly decompression of response bodies for CRS inspection"
+  long_description: |
+    Decompresses gzip/deflate compressed HTTP response bodies so that CRS
+    response rules can inspect the actual content. Without this plugin,
+    compressed responses bypass response body inspection rules.
+  type: "official"
+  category: "utility"
+  status: "being-tested"
+  license: "Apache-2.0"
+  authors:
+    - name: "OWASP CRS Team"
+      url: "https://coreruleset.org"
+  repository: "https://github.com/coreruleset/body-decompress-plugin"
+  keywords:
+    - "decompression"
+    - "response-body"
+    - "gzip"
+
+rule_id_range:
+  start: 9503000
+  end: 9503999
+
+compatibility:
+  crs_version: ">=4.0.0"
+  engines:
+    - "modsecurity2"
+    - "modsecurity3"
+
+configuration:
+  file: "plugins/body-decompress-config-before.conf"
+  variables:
+    - name: "tx.body-decompress-plugin_enabled"
+      type: "boolean"
+      default: 1
+      description: "Enable or disable response body decompression"
+
+    - name: "tx.body-decompress-plugin_max_data_size_bytes"
+      type: "integer"
+      default: 102400
+      description: "Maximum decompressed data size in bytes"
+      min: 1024
+      max: 10485760
+      example: 102400

examples/fake-bot-plugin.yaml

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+# OWASP CRS Plugin Descriptor
+# https://github.com/coreruleset/plugin-registry
+
+schema_version: 1
+
+plugin:
+  name: "fake-bot-plugin"
+  description: "Detects fake search engine bots by verifying crawler IP addresses"
+  long_description: |
+    Identifies HTTP requests that claim to be from known search engine crawlers
+    (Googlebot, Bingbot, etc.) but originate from IP addresses not belonging to
+    those search engines. Helps protect against scraping and abuse from clients
+    impersonating legitimate bots.
+  type: "official"
+  category: "detection"
+  status: "tested"
+  license: "Apache-2.0"
+  authors:
+    - name: "OWASP CRS Team"
+      url: "https://coreruleset.org"
+  repository: "https://github.com/coreruleset/fake-bot-plugin"
+  homepage: "https://coreruleset.org/docs/plugins/"
+  keywords:
+    - "bot-detection"
+    - "fake-bot"
+    - "crawler"
+    - "security"
+
+rule_id_range:
+  start: 9504000
+  end: 9504999
+
+compatibility:
+  crs_version: ">=4.0.0"
+  engines:
+    - "modsecurity2"
+    - "modsecurity3"
+    - "coraza"
+
+configuration:
+  file: "plugins/fake-bot-config.conf"
+  variables:
+    - name: "tx.fake-bot-plugin_enabled"
+      type: "boolean"
+      default: 1
+      description: "Enable or disable the fake bot detection plugin (0 to disable)"
+
+    - name: "tx.fake-bot-plugin_whitelist_broken_apple_devices"
+      type: "boolean"
+      default: 0
+      description: "Whitelist broken Apple devices that incorrectly identify as Googlebot"

examples/wordpress-rule-exclusions-plugin.yaml

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+# OWASP CRS Plugin Descriptor
+# https://github.com/coreruleset/plugin-registry
+
+schema_version: 1
+
+plugin:
+  name: "wordpress-rule-exclusions-plugin"
+  description: "CRS rule exclusions for WordPress applications"
+  long_description: |
+    Provides targeted rule exclusions to eliminate false positives when
+    running OWASP CRS in front of WordPress sites. Covers the WordPress
+    admin panel, REST API, and common plugin/theme patterns.
+  type: "official"
+  category: "rule-exclusion"
+  status: "tested"
+  license: "Apache-2.0"
+  authors:
+    - name: "OWASP CRS Team"
+      url: "https://coreruleset.org"
+  repository: "https://github.com/coreruleset/wordpress-rule-exclusions-plugin"
+  keywords:
+    - "wordpress"
+    - "cms"
+    - "rule-exclusion"
+    - "false-positive"
+
+rule_id_range:
+  start: 9507000
+  end: 9507999
+
+compatibility:
+  crs_version: ">=4.0.0"
+  engines:
+    - "modsecurity2"
+    - "modsecurity3"
+    - "coraza"
+
+configuration:
+  file: "plugins/wordpress-rule-exclusions-config.conf"
+  variables:
+    - name: "tx.wordpress-rule-exclusions-plugin_enabled"
+      type: "boolean"
+      default: 1
+      description: "Enable or disable WordPress rule exclusions (0 to disable)"