This request is required to be conditional; try using "If-Match".
Responses with the 428 status code MUST NOT be stored by a cache. 4. 429 Too Many Requests The 429 status code indicates that the user has sent too many requests in a given amount of time ("rate limiting"). The response representations SHOULD include details explaining the condition, and MAY include a Retry-After header indicating how long to wait before making a new request. For example: HTTP/1.1 429 Too Many Requests Content-Type: text/html Retry-After: 3600 Too Many Requests Too Many RequestsI only allow 50 requests per hour to this Web site per logged in user. Try again soon.
Note that this specification does not define how the origin server identifies the user, nor how it counts requests. For example, an origin server that is limiting request rates can do so based upon counts of requests on a per-resource basis, across the entire server, or even among a set of servers. Likewise, it might identify the user by its authentication credentials, or a stateful cookie. Responses with the 429 status code MUST NOT be stored by a cache. Nottingham & Fielding Standards Track [Page 3] RFC 6585 Additional HTTP Status Codes April 2012 5. 431 Request Header Fields Too Large The 431 status code indicates that the server is unwilling to process the request because its header fields are too large. The request MAY be resubmitted after reducing the size of the request header fields. It can be used both when the set of request header fields in total is too large, and when a single header field is at fault. In the latter case, the response representation SHOULD specify which header field was too large. For example: HTTP/1.1 431 Request Header Fields Too Large Content-Type: text/html Request Header Fields Too Large Request Header Fields Too LargeThe "Example" header was too large.
Responses with the 431 status code MUST NOT be stored by a cache. 6. 511 Network Authentication Required The 511 status code indicates that the client needs to authenticate to gain network access. The response representation SHOULD contain a link to a resource that allows the user to submit credentials (e.g., with an HTML form). Note that the 511 response SHOULD NOT contain a challenge or the login interface itself, because browsers would show the login interface as being associated with the originally requested URL, which may cause confusion. The 511 status SHOULD NOT be generated by origin servers; it is intended for use by intercepting proxies that are interposed as a means of controlling access to the network. Responses with the 511 status code MUST NOT be stored by a cache. Nottingham & Fielding Standards Track [Page 4] RFC 6585 Additional HTTP Status Codes April 2012 6.1. The 511 Status Code and Captive Portals The 511 status code is designed to mitigate problems caused by "captive portals" to software (especially non-browser agents) that is expecting a response from the server that a request was made to, not the intervening network infrastructure. It is not intended to encourage deployment of captive portals -- only to limit the damage caused by them. A network operator wishing to require some authentication, acceptance of terms, or other user interaction before granting access usually does so by identifying clients who have not done so ("unknown clients") using their Media Access Control (MAC) addresses. Unknown clients then have all traffic blocked, except for that on TCP port 80, which is sent to an HTTP server (the "login server") dedicated to "logging in" unknown clients, and of course traffic to the login server itself. For example, a user agent might connect to a network and make the following HTTP request on TCP port 80: GET /index.htm HTTP/1.1 Host: www.example.com Upon receiving such a request, the login server would generate a 511 response: HTTP/1.1 511 Network Authentication Required Content-Type: text/html Network Authentication RequiredYou need to authenticate with the local network in order to gain access.
Here, the 511 status code assures that non-browser clients will not interpret the response as being from the origin server, and the META HTML element redirects the user agent to the login server. Nottingham & Fielding Standards Track [Page 5] RFC 6585 Additional HTTP Status Codes April 2012 7. Security Considerations 7.1. 428 Precondition Required The 428 status code is optional; clients cannot rely upon its use to prevent "lost update" conflicts. 7.2. 429 Too Many Requests When a server is under attack or just receiving a very large number of requests from a single party, responding to each with a 429 status code will consume resources. Therefore, servers are not required to use the 429 status code; when limiting resource usage, it may be more appropriate to just drop connections, or take other steps. 7.3. 431 Request Header Fields Too Large Servers are not required to use the 431 status code; when under attack, it may be more appropriate to just drop connections, or take other steps. 7.4. 511 Network Authentication Required In common use, a response carrying the 511 status code will not come from the origin server indicated in the request's URL. This presents many security issues; e.g., an attacking intermediary may be inserting cookies into the original domain's name space, may be observing cookies or HTTP authentication credentials sent from the user agent, and so on. However, these risks are not unique to the 511 status code; in other words, a captive portal that is not using this status code introduces the same issues. Also, note that captive portals using this status code on a Secure Socket Layer (SSL) or Transport Layer Security (TLS) connection (commonly, port 443) will generate a certificate error on the client. Nottingham & Fielding Standards Track [Page 6] RFC 6585 Additional HTTP Status Codes April 2012 8. IANA Considerations The HTTP Status Codes registry has been updated with the following entries: Value: 428 Description: Precondition Required Reference: [RFC6585] Value: 429 Description: Too Many Requests Reference: [RFC6585] Value: 431 Description: Request Header Fields Too Large Reference: [RFC6585] Value: 511 Description: Network Authentication Required Reference: [RFC6585] 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 9.2. Informative References [CORS] van Kesteren, A., Ed., "Cross-Origin Resource Sharing", W3C Working Draft WD-cors-20100727, July 2010, . [Favicon] Wikipedia, "Favicon", March 2012, . [OAuth2.0] Hammer-Lahav, E., Ed., Recordon, D., and D. Hardt, "The OAuth 2.0 Authorization Protocol", Work in Progress, March 2012. Nottingham & Fielding Standards Track [Page 7] RFC 6585 Additional HTTP Status Codes April 2012 [P3P] Marchiori, M., Ed., "The Platform for Privacy Preferences 1.0 (P3P1.0) Specification", W3C Recommendation REC-P3P-20020416, April 2002, . [RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault, "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791, March 2007. [RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)", RFC 4918, June 2007. [WIDGETS] Caceres, M., Ed., "Widget Packaging and XML Configuration", W3C Recommendation REC-widgets-20110927, September 2011, . [WebFinger] WebFinger Project, "WebFingerProtocol (Draft)", January 2010, . Nottingham & Fielding Standards Track [Page 8] RFC 6585 Additional HTTP Status Codes April 2012 Appendix A. Acknowledgements Thanks to Jan Algermissen and Julian Reschke for their suggestions and feedback. Appendix B. Issues Raised by Captive Portals Since clients cannot differentiate between a portal's response and that of the HTTP server that they intended to communicate with, a number of issues arise. The 511 status code is intended to help mitigate some of them. One example is the "favicon.ico" [Favicon] commonly used by browsers to identify the site being accessed. If the favicon for a given site is fetched from a captive portal instead of the intended site (e.g., because the user is unauthenticated), it will often "stick" in the browser's cache (most implementations cache favicons aggressively) beyond the portal session, so that it seems as if the portal's favicon has "taken over" the legitimate site. Another browser-based issue comes about when the Platform for Privacy Preferences [P3P] is supported. Depending on how it is implemented, it's possible a browser might interpret a portal's response for the p3p.xml file as the server's, resulting in the privacy policy (or lack thereof) advertised by the portal being interpreted as applying to the intended site. Other Web-based protocols such as WebFinger [WebFinger], Cross-Origin Resource Sharing [CORS], and Open Authorization [OAuth2.0] may also be vulnerable to such issues. Although HTTP is most widely used with Web browsers, a growing number of non-browsing applications use it as a substrate protocol. For example, Web Distributed Authoring and Versioning (WebDAV) [RFC4918] and Calendaring Extensions to WebDAV (CalDAV) [RFC4791] both use HTTP as the basis (for remote authoring and calendaring, respectively). Using these applications from behind a captive portal can result in spurious errors being presented to the user, and might result in content corruption, in extreme cases. Similarly, other non-browser applications using HTTP can be affected as well, e.g., widgets [WIDGETS], software updates, and other specialized software such as Twitter clients and the iTunes Music Store. It should be noted that it's sometimes believed that using HTTP redirection to direct traffic to the portal addresses these issues. However, since many of these uses "follow" redirects, this is not a good solution. Nottingham & Fielding Standards Track [Page 9] RFC 6585 Additional HTTP Status Codes April 2012 Authors' Addresses Mark Nottingham Rackspace EMail: mnot@mnot.net URI: http://www.mnot.net/ Roy T. Fielding Adobe Systems Incorporated 345 Park Ave. San Jose, CA 95110 USA EMail: fielding@gbiv.com URI: http://roy.gbiv.com/ Nottingham & Fielding Standards Track [Page 10]RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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