spec the format of a client_secret

api/identity/definitions/request_email_validation.yaml

@@ -20,7 +20,11 @@ example: {
 properties:
   client_secret:
     type: string
-    description: A unique string used to identify the validation attempt.
+    description: |
+      A unique string generated by the client, and used to identify the
+      validation attempt. It must be a string consisting of the characters
+      ``[0-9a-zA-Z.=_-]``. Its length must not exceed 255 characters and it
+      must not be empty.
     example: "monkeys_are_GREAT"
   email:
     type: string

api/identity/definitions/request_msisdn_validation.yaml

@@ -21,7 +21,11 @@ example: {
 properties:
   client_secret:
     type: string
-    description: A unique string used to identify the validation attempt.
+    description: |
+      A unique string generated by the client, and used to identify the
+      validation attempt. It must be a string consisting of the characters
+      ``[0-9a-zA-Z.=_-]``. Its length must not exceed 255 characters and it
+      must not be empty.
     example: "monkeys_are_GREAT"
   country:
     type: string