Add ability to supply different krb5 based on environment

Author: macsux

README.MD

@@ -99,7 +99,22 @@ Linux shell
 zip -ur KerberosBuildpack-linux-x64-v1.0.0.zip deps
 ```
 
+### Multiple environment control
 
+If krb5.conf need to be different across environments, multiple krb5.conf can be embedded into the buildpack by creating a folder structure similar to the following and applying steps above:
+
+```
+.
+├── KerberosBuildpack-linux-x64-v1.0.0.zip
+├── deps
+│   └── krb5
+│       ├── prod
+│       │   └── krb5.conf
+│       └── qa
+│           └── krb5.conf
+```
+
+ You can control which `krb5.conf` is used by setting `KRB_ENVIRONMENT` environmental variable so it matches the folder name.
 
 ## Troubleshooting
 

src/KerberosBuildpack/KerberosBuildpack.cs

@@ -17,13 +17,20 @@ protected override void Apply(AbsolutePath buildPath, AbsolutePath cachePath, Ab
             EnvironmentalVariables["KRB5_KTNAME"] = "/home/vcap/app/.krb5/service.keytab";
             EnvironmentalVariables["KRB5_CLIENT_KTNAME"] = "/home/vcap/app/.krb5/service.keytab";
 
+            
+            
             Directory.CreateDirectory(krb5TargetDir);
 
             var currentAssemblyDir = ((AbsolutePath)Assembly.GetExecutingAssembly().Location).Parent;
             var buildpackDir = currentAssemblyDir.Parent;
             var sidecarSrcDir = buildpackDir / "deps"  / "sidecar";
             var sidecarTargetDir = myDependenciesDirectory / "sidecar";
             var krb5SourceDir = buildpackDir / "deps" / ".krb5";
+            var krb5Environment = Environment.GetEnvironmentVariable("KRB_ENVIRONMENT");
+            if (krb5Environment != null)
+            {
+                krb5SourceDir = krb5SourceDir / krb5Environment;
+            }
             if (Directory.Exists(krb5SourceDir))
             {
                 FileSystemTasks.CopyDirectoryRecursively(krb5SourceDir, krb5TargetDir, DirectoryExistsPolicy.Merge, FileExistsPolicy.Skip);