Put the path to client_secrets in a config option.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148214513

java/google/registry/config/RegistryConfig.java

@@ -19,6 +19,7 @@ import static google.registry.config.ConfigUtils.makeUrl;
 import static google.registry.config.YamlUtils.getConfigSettings;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Optional;
 import com.google.common.base.Supplier;
 import com.google.common.collect.ImmutableList;
@@ -974,6 +975,17 @@ public final class RegistryConfig {
       return "/tos";
     }
 
+    /**
+     * Returns the name of the OAuth2 client secrets file.
+     *
+     * <p>This is the name of a resource relative to the root of the class tree.
+     */
+    @Provides
+    @Config("clientSecretFilename")
+    public static String provideClientSecretFilename(RegistryConfigSettings config) {
+      return config.registryTool.clientSecretFilename;
+    }
+
     /**
      * Returns the help text to be used by RDAP.
      *
@@ -1174,6 +1186,12 @@ public final class RegistryConfig {
     return Duration.standardDays(CONFIG_SETTINGS.get().registryPolicy.contactAutomaticTransferDays);
   }
 
+  /** Provided for testing. */
+  @VisibleForTesting
+  public static String getClientSecretFilename() {
+    return CONFIG_SETTINGS.get().registryTool.clientSecretFilename;
+  }
+
   /**
    * Memoizes loading of the {@link RegistryConfigSettings} POJO.
    *