Return application/problem+json format errors and provide error endpoint

to dereference error codes.

endpoints/api/error.py

@@ -0,0 +1,56 @@
+""" Error details API """
+from flask import url_for
+from enum import Enum
+
+from endpoints.api import (resource, nickname, ApiResource, NotFound, path_param,
+                           define_json_response, ApiErrorType, ERROR_DESCRIPTION)
+
+
+def error_view(error_type):
+  return {
+    'type': url_for('error', error_type=error_type, _external=True),
+    'title': error_type,
+    'description': ERROR_DESCRIPTION[error_type]
+  }
+
+
+@resource('/v1/error/<error_type>')
+@path_param('error_type', 'The error code identifying the type of error.')
+class Error(ApiResource):
+  """ Resource for manging an organization's teams. """
+  schemas = {
+    'ApiError': {
+      'type': 'object',
+      'description': 'Description of an error',
+      'required': [
+        'type',
+        'properties',
+        'title',
+      ],
+      'properties': {
+        'type': {
+          'type': 'string',
+          'description': 'A reference to the error type resource'
+        },
+        'title': {
+            'type': 'string',
+            'description': 'The title of the error. Can be used to uniquely identify the kind of error.',
+            'enum': list(ApiErrorType.__members__)
+        },
+        'description': {
+            'type': 'string',
+            'description': 'A more detailed description of the error that may include help for fixing the issue.'
+        }
+      },
+    },
+  }
+
+  @define_json_response('ApiError')
+  @nickname('getError')
+  def get(self, error_type):
+    """ Get a detailed description of the error """
+    if error_type in ERROR_DESCRIPTION.keys():
+        return error_view(error_type), 200
+    else:
+        raise NotFound()
+