An HTTP Status Code to Report Requester Impairment

Introduction This document specifies a Hypertext Transfer Protocol (HTTP) status code for use when a request is denied because the requester is impaired. This request code may be used to provide visibility in cases where one or more valid requests create a dangerous situation, there is a pattern of erratic requests with the potential for danger, or the requester is otherwise detected as impaired. Network-controlled devices are being used for beneficial but potentially dangerous activities such as construction and remote surgery. Identifying requester impairment is important for both accurately assessing the risk a given requester presents and preventing damage caused by a high-risk requester.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

420 Requester Impaired The status code 420 indicates that the server is denying the request as a consequence of evidence of requester impairment. The server in question might not be an origin server. An intermediate proxy closer to the requester may be in a better position to assess potential requester impairment. Such a proxy may refuse to forward the request and respond with this error code. There is no requirement that the requester be human. Certain AI systems can exhibit behaviors such as giving hallucinated, incorrect, and differing answers for a given input. Given the speed at which such AI operates, it is no less important to detect the impairment of AI requesters as human requesters. This response code provides greater visibility for requester impairment than the 403 Forbidden code. Such visibility will aid network monitoring for impaired requesters. This will improve remediation and risk assessment of possibly impaired requesters. 420 responses MUST include a Link header with a relation type of "status". This link is used by the recovered requester to obtain information about the server state and to signal to the server that the requester is recovered. Requesters SHOULD use this link when recovered before making subsequent requests unless a bearer token is used as described under and the server does not require usage of the link. Such responses MAY include the inputs or evidence used to determine impairment, but SHOULD NOT reveal information that a requester can use to evade impairment detection. A 420 response is non-cacheable by default, i.e., unless otherwise indicated by the method definition or explicit cache controls; see .

AI: An artificial intelligence system that is capable of making independent decisions without direct human control.
proxy: A server with a primary purpose of forwarding requests to other servers to process.

Example Response in Problem Details Format ; rel="status" Content-Type: application/problem+json Content-Language: en { "type": "https://example.com/erratic-requests", "title": "Requester Impaired: Erratic Behavior Detected.", "detail": "Potentially dangerous and erratic requests detected." } ]]>

IANA Considerations IANA is asked to update the HTTP Status Codes Registry with the following entry:

Code: 420
Description: Requester Impaired
Specification: This RFC

Security Considerations The usage of the link resource provided by the Link header to assert requester remediation assumes a requester or proxy that is trustworthy enough to halt requests and only access the link resource after requester remediation. If greater security is required, perhaps to enable an external system to remediate and validate the requester, a server MAY require an OAuth authorization bearer token to signal remediation of the requester. If a valid bearer token is required and missing, further requests SHOULD be rejected with a 403 Forbidden response code with the insufficient_scope error code and scope attribute naming the authorization token required as described in section 3.1. Once this authorization bearer token is validated the server MAY allow requests without using the Link provided in the 420 response, but MUST NOT respond to usage of the link as an error.