feat: document Maven Central mirror settings (#608)

Author: zlataovce

src/content/docs/paper/admin/reference/system-properties.md

@@ -244,9 +244,35 @@ It also remaps plugin CB calls to remove the version information.
 - **default**: `false`
 - **description**: Setting this to true indicates that you have agreed with [Mojang's EULA](https://aka.ms/MinecraftEULA), skipping `eula.txt` checks.
 
+#### org.bukkit.plugin.java.LibraryLoader.centralURL
+
+- **default**: `https://maven-central.storage-download.googleapis.com/maven2`
+- **description**: Sets the default central repository URL, from which plugins' dependencies declared using the [`libraries`](/paper/dev/plugin-yml#libraries) plugin.yml field are resolved. This is overridden by the [`PAPER_DEFAULT_CENTRAL_REPOSITORY`](#paper_default_central_repository) environment variable, if it is set.
+
+:::caution
+
+If you wish to configure this with Maven Central, use a mirror, as using Maven Central directly as a CDN is against the Maven Central Terms of Service, and you may hit rate limits.
+
+By default, this uses Google's NA mirror of Maven Central. You may also use region-specific mirrors listed [here](https://storage-download.googleapis.com/maven-central/index.html).
+
+:::
+
 ## List of environment variables
 
 #### PAPER_VELOCITY_SECRET
 
 - **default**: `unset`
 - **description**: Overrides the [`proxies.velocity.secret`](/paper/reference/global-configuration#proxies_velocity_secret) global configuration option.
+
+#### PAPER_DEFAULT_CENTRAL_REPOSITORY
+
+- **default**: `https://maven-central.storage-download.googleapis.com/maven2`
+- **description**: Sets the default central repository URL, from which plugins' dependencies declared using the [`libraries`](/paper/dev/plugin-yml#libraries) plugin.yml field are resolved. This overrides the [`org.bukkit.plugin.java.LibraryLoader.centralURL`](#orgbukkitpluginjavalibraryloadercentralurl) system property, if it is set.
+
+:::caution
+
+If you wish to configure this with Maven Central, use a mirror, as using Maven Central directly as a CDN is against the Maven Central Terms of Service, and you may hit rate limits.
+
+By default, this uses Google's NA mirror of Maven Central. You may also use region-specific mirrors listed [here](https://storage-download.googleapis.com/maven-central/index.html).
+
+:::

src/content/docs/paper/dev/getting-started/paper-plugins.md

@@ -157,6 +157,19 @@ Currently, you are able to add two different library types:
 [`JarLibrary`](jd:paper:io.papermc.paper.plugin.loader.library.impl.JarLibrary) and
 [`MavenLibraryResolver`](jd:paper:io.papermc.paper.plugin.loader.library.impl.MavenLibraryResolver).
 
+:::danger
+
+If you wish to resolve libraries from Maven Central, use a mirror, as using Maven Central directly as a CDN is against the Maven Central Terms of Service, and users of your plugin may hit rate limits.
+
+You should use Paper's default mirror, configured by the [`PAPER_DEFAULT_CENTRAL_REPOSITORY`](/paper/reference/system-properties#paper_default_central_repository) environment variable and [`org.bukkit.plugin.java.LibraryLoader.centralURL`](/paper/reference/system-properties#orgbukkitpluginjavalibraryloadercentralurl) system property:
+```java
+resolver.addRepository(new RemoteRepository.Builder("central", "default", MavenLibraryResolver.MAVEN_CENTRAL_DEFAULT_MIRROR).build());
+```
+
+Using the Maven Central repository (i.e. `*.maven.org` or `*.maven.apache.org`) will cause a warning to be shown in the console.
+
+:::
+
 ## Differences
 
 ### Bukkit serialization system

src/content/docs/paper/dev/getting-started/plugin-yml.mdx

@@ -114,12 +114,6 @@ The prefix of the plugin. This is what will be displayed in the log instead of t
 
 ### libraries
 
-:::caution
-
-The use of this feature is *currently* against Maven Central's TOS. However, this feature is very likely to stay.
-
-:::
-
 This is a list of libraries that your plugin depends on. These libraries will be downloaded from the Maven Central repository and added to the classpath.
 This removes the need to shade and relocate the libraries.
 
@@ -129,6 +123,12 @@ libraries:
   - com.google.code.gson:gson:2.8.6
 ```
 
+:::note
+
+The central repository is configurable using the [`PAPER_DEFAULT_CENTRAL_REPOSITORY`](/paper/reference/system-properties#paper_default_central_repository) environment variable and [`org.bukkit.plugin.java.LibraryLoader.centralURL`](/paper/reference/system-properties#orgbukkitpluginjavalibraryloadercentralurl) system property.
+
+:::
+
 ### permissions
 
 This is a list of permissions that your plugin uses. This is useful for plugins that use permissions to restrict access to certain features.