Validate request

1. Validate request using JSON schema
   
   1. In case validation failed - generate 422 error

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "type": "object",
  "properties": {
    "verification_code": {
      "type": "string"
    }
  },
  "required": [
    "verification_code"
  ],
  "additionalProperties": false
}

Authorize user

1. Verify the validity of access token
2. Check user scopes declaration_request:sign in order to perform this action
   1. In case error - generate 401 response

Verify code

1. 1. Verify the validity of verification code
      1. In case error - generate 401 response

...