try creating new decorator

addon/configuration.js

@@ -4,13 +4,54 @@ import { get, computed } from '@ember/object';
 const NAMESPACE = 'providers';
 let configuration = {};
 
+const getValue = function (configKey) {
+  const configNamespace = NAMESPACE + '.' + this.get('name');
+  const propertyPath = configNamespace + '.' + configKey;
+  const configuration = getConfiguration();
+  return get(configuration, propertyPath);
+};
+
 function configurable(configKey, defaultValue) {
-  return computed(function configurableComputed() {
-    var configNamespace = NAMESPACE + '.' + this.get('name');
-    var propertyPath = configNamespace + '.' + configKey;
-    let configuration = getConfiguration();
-    var value = get(configuration, propertyPath);
+  // want to somehow determine if should return legacy or new decorator
+  return configurableLegacy(configKey, defaultValue);
+}
+
+function configurableDecorator(configKey, defaultValue) {
+  return function (_target, _key, descriptor) {
+    const originalGetter = descriptor.get;
+    const getter = function () {
+      const value = getValue.call(this, configKey);
+
+      if (typeof value === 'undefined') {
+        if (typeof defaultValue !== 'undefined') {
+          if (typeof defaultValue === 'function') {
+            return defaultValue.call(this);
+          } else {
+            return defaultValue;
+          }
+        } else if (typeof originalGetter === 'function') {
+          return originalGetter.call(this);
+        } else {
+          throw new Error(
+            `Expected configuration value ${configKey} to be defined for provider named ${this.name}`
+          );
+        }
+      }
+
+      return value;
+    };
 
+    return {
+      get: getter,
+      enumberable: false,
+      configurable: true,
+    };
+  };
+}
+
+function configurableLegacy(configKey, defaultValue) {
+  return computed(function configurableComputed() {
+    const value = getValue.call(this, configKey);
     if (typeof value === 'undefined') {
       if (typeof defaultValue !== 'undefined') {
         if (typeof defaultValue === 'function') {
@@ -39,6 +80,12 @@ function getConfiguration() {
   return configuration;
 }
 
-export { configurable, configure, getConfiguration };
+export {
+  configurable,
+  configurableLegacy,
+  configurableDecorator,
+  configure,
+  getConfiguration,
+};
 
 export default {};

tests/unit/configuration-test.js

@@ -1,7 +1,11 @@
 /* eslint-disable ember/no-classic-classes, ember/no-get */
 import EmberObject from '@ember/object';
 import { run } from '@ember/runloop';
-import { configurable, configure } from 'torii/configuration';
+import {
+  configurable,
+  configurableDecorator,
+  configure,
+} from 'torii/configuration';
 import { module, test } from 'qunit';
 
 module('Unit | Configuration', function (hooks) {
@@ -19,20 +23,20 @@ module('Unit | Configuration', function (hooks) {
 
   const Testable2 = class extends EmberObject {
     name = 'test';
-    @configurable('apiKey') required;
-    @configurable('scope', 'email') defaulted;
+    @configurableDecorator('apiKey') required;
+    @configurableDecorator('scope', 'email') defaulted;
     defaultedFunctionValue = 'found-via-get';
 
     // not supported by @computed due to limitations in decorators
-    @configurable('redirectUri')
+    @configurableDecorator('redirectUri')
     get defaultedFunction() {
       return this.get('defaultedFunctionValue');
     }
   };
 
   hooks.beforeEach(function () {
     testable1 = Testable.create();
-    testable2 = Testable2.create();
+    testable2 = new Testable2();
     testables = { testable1, testable2 };
   });
 
@@ -64,7 +68,7 @@ module('Unit | Configuration', function (hooks) {
 
       assert.ok(threw, 'read threw');
       assert.ok(
-        /Expected configuration value apiKey to be defined for provider named test/.test(
+        /Expected configuration value "?apiKey"? to be defined for provider named "?test"?/.test(
           message
         ),
         'did not have proper error: ' + message