Add new site page "Third-party Integrations"

Where new supplier is described.

src/site/markdown/third-party-integrations.md

@@ -0,0 +1,72 @@
+# Third-party integrations
+<!---
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements.  See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License.  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+-->
+
+Maven Resolver provided option for third-party integration using `ServiceLocator` (SL)
+from the beginning. Back when SL was implemented, the DI container in use with Resolver and
+Maven was the Plexus DI container, that had its own limitations: no constructor injection
+among others. Hence, the two was somewhat aligned with each other. Today, with Sisu DI, 
+this is not true anymore: we want to use constructor injection for components, but
+SL is always getting into our way forcing us to always add default constructor to components.
+Hence, decision was made, and SL was deprecated while ago, and is about to be 
+dropped in Resolver 2.0.0 release.
+
+Resolver does provide alternative solution for those third-party integrations, where the
+(recommended) Sisu DI is not available or cannot be used for some reason. All the
+resolver integrations starting with release 1.9.15 can start migrating off the SL
+to current solution described below.
+
+## Maven Resolver Supplier
+
+A new simple module `maven-resolver-supplier` serves the purpose to "bootstrap" resolver instance
+when there is no desire to use [Eclipse Sisu](https://eclipse.dev/sisu/) DI. It provides one simple class 
+`org.eclipse.aether.supplier.RepositorySystemSupplier` that implements `Supplier<RepositorySystem>`
+and supplies ready-to-use `RepositorySystem` instances. The `RepositorySystemSession` should be
+created using the `org.apache.maven.repository.internal.MavenRepositorySystemUtils#newSession()` method
+and local repository added to it in usual way (there is no change in this area).
+
+The supplier class is written in a way, to allow easy customization if needed: just extend the class and override
+method as needed (all methods are protected).
+
+Consumer/users of this module **must provide SLF4J implementation** in classpath. Resolver uses `slf4j-api` for 
+logging purposes, but this module does NOT provide any implementation for it as a dependency. 
+It is the consumer/user obligation to provide one at runtime.
+
+Version of `maven-resolver-supplier` artifact in use **must be strictly aligned** with other Resolver artifacts 
+on classpath.
+
+## Resolver configuration
+
+By default, "full resolver experience" is provided:
+* for connector, the connector-basic is provided
+* for transport the two transport-file and transport-http implementations are provided. If Wagon is needed, add
+  transport-wagon as dependency (see Extending Resolver below).
+
+The supplier will provide fully usable instance. To configure resolver, use session user (or 
+configuration) properties, when constructing session. All the configuration options are available as 
+[listed here](https://maven.apache.org/resolver/configuration.html).
+
+## Extending Resolver
+
+Extending supplied resolver is simple, and basically requires same three steps for whatever extra you want to include
+(like Wagon transport, distributed locking, etc).
+
+* First, you need to include needed module (with transitive deps) to your dependencies.
+* Second, you need to customize `RepositorySystemSupplier` by extending it, and to make new components 
+  available (by adding `WagonTransporterFactory` to transport factories, or distributed lock factories to lock factories).
+* Third, you need to configure session (via user or configuration properties) to make Resolver use newly added components.
+

src/site/site.xml

@@ -32,6 +32,7 @@ under the License.
       <item name="Expected Checksums" href="expected-checksums.html"/>
       <item name="About Local Repository" href="local-repository.html"/>
       <item name="Remote Repository Filtering" href="remote-repository-filtering.html"/>
+      <item name="Third-party Integrations" href="third-party-integrations.html"/>
       <item name="Maven 3.8.x" href="maven-3.8.x.html"/>
       <item name="JavaDocs" href="apidocs/index.html"/>
       <item name="Source Xref" href="xref/index.html"/>