refactor(gcb): Further clean-up of GCB config (#742)

Given that we are enforcing a non-null account name and project
downstream, let's enforce them at object creation to make things
cleaner.

This commit also removes the subscriptionName field; it is
part of the config but not needed by igor, so there's no sense
mapping it.

Finally, make jsonKey an optional to better reflect that it is
optional (instead of treating an empty string as a sentinel
value).

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

igor-web/src/main/java/com/netflix/spinnaker/igor/config/GoogleCloudBuildProperties.java

@@ -16,6 +16,7 @@
 
 package com.netflix.spinnaker.igor.config;
 
+import com.google.common.base.Preconditions;
 import com.google.common.base.Strings;
 import com.netflix.spinnaker.fiat.model.resources.Permissions;
 import com.netflix.spinnaker.igor.model.BuildServiceProvider;
@@ -43,25 +44,22 @@ public List<BuildService> getGcbBuildServices() {
   @NonnullByDefault
   @Value
   public static final class Account implements BuildService {
+    private static final String ERROR_TEMPLATE = "Missing required field for GCB account %s: %s";
+
     private final String name;
     private final String project;
-    private final String subscriptionName;
-    private final String jsonKey;
+    private final Optional<String> jsonKey;
     private final Permissions permissions;
 
     @Builder
     @ConstructorBinding
     @ParametersAreNullableByDefault
-    public Account(
-        String name,
-        String project,
-        String subscriptionName,
-        String jsonKey,
-        Permissions.Builder permissions) {
-      this.name = Strings.nullToEmpty(name);
-      this.project = Strings.nullToEmpty(project);
-      this.subscriptionName = Strings.nullToEmpty(subscriptionName);
-      this.jsonKey = Strings.nullToEmpty(jsonKey);
+    public Account(String name, String project, String jsonKey, Permissions.Builder permissions) {
+      this.name = Preconditions.checkNotNull(Strings.emptyToNull(name), ERROR_TEMPLATE, "", "name");
+      this.project =
+          Preconditions.checkNotNull(
+              Strings.emptyToNull(project), ERROR_TEMPLATE, this.name, "project");
+      this.jsonKey = Optional.ofNullable(Strings.emptyToNull(jsonKey));
       this.permissions =
           Optional.ofNullable(permissions)
               .map(Permissions.Builder::build)

igor-web/src/main/java/com/netflix/spinnaker/igor/gcb/GoogleCloudBuildAccountFactory.java

@@ -46,10 +46,10 @@ GoogleCloudBuildAccount build(GoogleCloudBuildProperties.Account account) {
   }
 
   private GoogleCredentials getCredentials(GoogleCloudBuildProperties.Account account) {
-    if (account.getJsonKey().isEmpty()) {
-      return credentialService.getApplicationDefault();
+    if (account.getJsonKey().isPresent()) {
+      return credentialService.getFromKey(account.getJsonKey().get());
     } else {
-      return credentialService.getFromKey(account.getJsonKey());
+      return credentialService.getApplicationDefault();
     }
   }
 }