Handle JSONified errors while registering

Closes #617

src/services/errors/errors.js

@@ -1,3 +1,5 @@
+import { humanizeErrors } from '../../modules/errors'
+
 export function StatusCodeError (statusCode, body, options, response) {
   this.name = 'StatusCodeError'
   this.statusCode = statusCode
@@ -12,3 +14,36 @@ export function StatusCodeError (statusCode, body, options, response) {
 }
 StatusCodeError.prototype = Object.create(Error.prototype)
 StatusCodeError.prototype.constructor = StatusCodeError
+
+export class RegistrationError extends Error {
+  constructor (error) {
+    super()
+    if (Error.captureStackTrace) {
+      Error.captureStackTrace(this)
+    }
+
+    try {
+      // the error is probably a JSON object with a single key, "errors", whose value is another JSON object containing the real errors
+      if (typeof error === 'string') {
+        error = JSON.parse(error)
+        if (error.hasOwnProperty('error')) {
+          error = JSON.parse(error.error)
+        }
+      }
+
+      if (typeof error === 'object') {
+        // replace ap_id with username
+        if (error.ap_id) {
+          error.username = error.ap_id
+          delete error.ap_id
+        }
+        this.message = humanizeErrors(error)
+      } else {
+        this.message = error
+      }
+    } catch (e) {
+      // can't parse it, so just treat it like a string
+      this.message = error
+    }
+  }
+}