Publish (multiple) classic web application projects in multiple configurations to an output folder

ci-publish.proj.xml

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">

  <!-- CONFIGURE the configurations to publish for here -->
  <PropertyGroup>
    <ConfigurationsToPublish>Release;CD;UAT;Customer1;Customer2</ConfigurationsToPublish>
  </PropertyGroup>
  
  <!-- CONFIGURE the web projects to publish here. -->
  <ItemGroup>
    <ProjectToPublish Include="**\*.Web.csproj" />
  </ItemGroup>
  
  <!-- WARNING: Be careful with the rest of this file -->
  
  <PropertyGroup>
    <!-- Default artifact staging directory when built via VSTS / TFS agent -->
    <PublishBaseDir Condition="'$(PublishBaseDir)' == '' and '$(BUILD_ARTIFACTSTAGINGDIRECTORY)' != '' ">$(BUILD_ARTIFACTSTAGINGDIRECTORY)</PublishBaseDir>
	
    <!-- If not built on a known agent, use a "publish" subdir next to this file -->
    <PublishBaseDir Condition="'$(PublishBaseDir)' == ''">$(MSBuildThisFileDirectory)publish\</PublishBaseDir>
	
    <!-- Normalize directory if set manually or through ENV var -->
    <PublishBaseDir Condition="!HasTrailingSlash('$(PublishBaseDir)')">$(PublishBaseDir)\</PublishBaseDir>
  </PropertyGroup>

  <Target Name="Build" DependsOnTargets="_PublishProjectsOnInnerBuild">
    <ItemGroup Condition="'$(Configuration)' == ''">
      <InnerBuildConfiguration Include="$(ConfigurationsToPublish)" />
    </ItemGroup>
    <!-- Call inner build -->
    <MSBuild Projects="$(MSBuildProjectFile)" Targets="Build" Properties="Configuration=%(InnerBuildConfiguration.Identity)" Condition="'$(Configuration)' == ''" />
  </Target>

  <!-- Preprare current configuration for publish (inner build). If Configuration isn't set, don't do anything (=> outer build) -->
  <Target Name="_PublishProjectsOnInnerBuild" Condition="'$(Configuration)' != ''">
    <ItemGroup>
      <ResolvedProjectToPublish Include="@(ProjectToPublish)">
        <PublishUrl>$(PublishBaseDir)%(Filename)\$(Configuration)\</PublishUrl>
        <IntermediateOutputPath>%(RootDir)%(Directory)obj\$(Configuration)\</IntermediateOutputPath>
        <PublishProfileUrl>%(ResolvedProjectToPublish.IntermediateOutputPath)GeneratedProfile.pubxml</PublishProfileUrl>
      </ResolvedProjectToPublish>
    </ItemGroup>
    
    <MakeDir Directories="@(ResolvedProjectToPublish->'%(IntermediateOutputPath)')" />
    
    <MSBuild Projects="$(MSBuildProjectFile)"
             Targets="_PublishProject" 
             Properties="Configuration=$(Configuration);TargetProject=%(ResolvedProjectToPublish.Identity);PublishProfileUrl=%(ResolvedProjectToPublish.PublishProfileUrl);PublishUrl=%(ResolvedProjectToPublish.PublishUrl)" />
  </Target>

  <!-- expects $(Configuration), $(TargetProject), $(PublishProfileUrl) and $(PublishUrl) to be set (inner build) -->
  <Target Name="_PublishProject">
    <PropertyGroup>
      <PublishProfile>
        <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
          <PropertyGroup>
            <WebPublishMethod>FileSystem</WebPublishMethod>
            <LastUsedBuildConfiguration>$(Configuration)</LastUsedBuildConfiguration>
            <LastUsedPlatform>Any CPU</LastUsedPlatform>
            <SiteUrlToLaunchAfterPublish />
            <ExcludeApp_Data>False</ExcludeApp_Data>
            <publishUrl>$(PublishUrl)</publishUrl>
            <DeleteExistingFiles>True</DeleteExistingFiles>
          </PropertyGroup>
        </Project>
      </PublishProfile>
      
      <PublishBuildProperties>
        Configuration=$(Configuration);
        DeployOnBuild=true;
        PublishProfile=$([System.IO.Path]::GetFullPath('$(PublishProfileUrl)'))
      </PublishBuildProperties>
    </PropertyGroup>

    <WriteLinesToFile File="$(PublishProfileUrl)" Lines="$(PublishProfile)" Overwrite="true" />
    <MSBuild Projects="$(TargetProject)" Targets="Build" Properties="$(PublishBuildProperties)" />
  </Target>
  
</Project>