Use Cases for Authentication of Web Bots
draft-nottingham-webbotauth-use-cases-02

Network Working Group                                      M. Nottingham
Internet-Draft                                              1 April 2026
Intended status: Standards Track                                        
Expires: 3 October 2026

                Use Cases for Authentication of Web Bots
                draft-nottingham-webbotauth-use-cases-02

Abstract

   This draft outlines use cases for authentication for bot clients on
   the Web, to help inform discussions regarding the scope and intent of
   the WebBotAuth Working Group.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-nottingham-webbotauth-use-
   cases/.

   information can be found at https://mnot.github.io/I-D/.

   Source for this draft and an issue tracker can be found at
   https://github.com/mnot/I-D/labels/webbotauth-use-cases.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 3 October 2026.

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Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Web Site Use Cases  . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Mitigating Volumetric Abuse by Bots . . . . . . . . . . .   3
     2.2.  Controlling Access by Bots  . . . . . . . . . . . . . . .   4
     2.3.  Providing Different Content to Bots . . . . . . . . . . .   5
     2.4.  Auditing Bot Behaviour  . . . . . . . . . . . . . . . . .   6
     2.5.  Classifying Traffic . . . . . . . . . . . . . . . . . . .   6
     2.6.  Authenticating Site Services  . . . . . . . . . . . . . .   7
   3.  Bot Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  IP Address Mobility . . . . . . . . . . . . . . . . . . .   7
     3.2.  Sharing IP Addresses  . . . . . . . . . . . . . . . . . .   8
     3.3.  Robots.txt Alignment  . . . . . . . . . . . . . . . . . .   8
     3.4.  Conveying Contextual Information  . . . . . . . . . . . .   8
   4.  Next Steps  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Bot Differences  . . . . . . . . . . . . . . . . . .   9
     A.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     A.2.  Relationship  . . . . . . . . . . . . . . . . . . . . . .  10
     A.3.  Reputation  . . . . . . . . . . . . . . . . . . . . . . .  10
     A.4.  Agency  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The Web Bot Auth (WebBotAuth) Working Group has been chartered to
   "standardize methods for cryptographically authenticating automated
   clients and providing additional information about their operators to
   Web sites."

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   Initial discussions have revealed some disagreement about the group's
   scope.  Section 2 explores the use cases for authentication of non-
   browser clients, to help inform those discussions.  Section 4
   suggests some further questions for consideration.

2.  Web Site Use Cases

   This section explores use cases that Web sites might have for
   authenticating bots, including a discussion of any current mechanisms
   that they use to meet the use case.

   Because there is some question about the "additional information"
   facility in the charter, each use case also assesses whether it's
   necessary to identify a real-world entity associated with the bot to
   meet the use case (since that is the most common use of such a
   facility).

   Each use case also summarises how controversial addressing it is
   perceived to be.

   This draft does not take a position on whether all of the use cases
   should be addressed by the group.  Potential alternative solutions to
   the implied requirements are also not considered here.

2.1.  Mitigating Volumetric Abuse by Bots

   Some bots make requests at rates that cause operational issues for
   Web sites.  This may be intentional (e.g., traffic from "botnets" and
   other attacks) or unintentional (due to overly simple or
   inconsiderate implementation).  It appears that both the number of
   such bots and the rate at which they make requests are increasing.

   While sites can take measures to mitigate the impact of this traffic
   (e.g., caching), these are only partially effective; some resources
   are uncacheable, and generating representations of some HTTP
   resources can incur much higher costs -- both in terms of computation
   and economics.  In general, serving such great volumes of traffic can
   consume significant resources, in terms of both infrastructure and
   bandwidth.

   Currently, a site that experiences such traffic most often blocks
   unwelcome clients by IP address.  This has the effect of blocking
   other uses of that IP address, both at that time and into the
   indefinite future.  It also offers little recourse for incorrectly
   blocked clients, since they have no information about why they were
   blocked or what they should do about it.

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   This use case does not require identifying a specific bot or
   associating it with a real-world entity, provided that the site
   considers abusiveness a feature of behaviour, not identity.  It also
   does not require discriminating between bots and non-bot users; only
   the problematic behaviour is targeted.

   Addressing this use case does not appear to be overly controversial,
   because it is widely recognised that a site needs to operate with
   reasonable efficiency to provide both its operators and its users a
   benefit.

2.2.  Controlling Access by Bots

   Some sites wish to make access by bots to the resources they provided
   to browsers conditional upon the identity or features of the bot.
   This might be for a variety of reasons; they may wish to:

   *  Only allow access by bots on an allow list;

   *  Disallow access to bots on an explicit deny list;

   *  Condition access upon meeting some criteria (e.g., non-profit,
      certification by a third party);

   *  Condition access upon participation in some scheme or protocol
      (e.g., payment for access);

   Note that the first two imply some notion of bots being tied to a
   real-world identity, whereas the remaining do not necessarily require
   it.

   Currently, sites most often use a combination of the Robots Exclusion
   Protocol (including robots.txt) and IP address blocking to control
   access by bots.

   The Robots Exclusion Protocol provides a means for sites to
   communicate preferences to bots about their behaviour.  Although this
   is a useful and sometimes necessary function, it does not allow for
   enforcement of those preferences.

   Enforcement is achieved primarily through blocking non-conforming
   clients.  The limitations of IP address blocking are discussed in
   Section 2.1.

   This use case has been disputed.  While blocking certain bots by IP
   address is widespread in practice, concerns have been expressed that
   standardising an authentication mechanism for bots might result in a
   Web where all bots might need to authenticate, leading to increased

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   difficulty in introducing new bots.  In some markets, this outcome
   could create pressure towards centralisation, due to heightened
   barriers to entry.

   Another controversy is that giving sites a more fine-grained
   capability to block bots is a change in the balance of power on the
   Web. Some perceive that as justified, given factors like the
   introduction of AI and what they perceive as an onslaught of bot
   traffic.  Others see it as an overreach that may impinge upon users'
   ability to consume content as they desire -- for example, using
   accessibility tools or autonomous agents.

   Finally, some see bots as a way of keeping powerful sites in check,
   and therefore measures to curtail their activity is portrayed as
   concentrating that power.  However, it should be noted that there are
   also powerful bots that can be seen to have disproportionate power
   over sites, and so there is not necessarily a clear bias here.

2.3.  Providing Different Content to Bots

   Some sites may wish to tailor the content they serve to bots (either
   selectively or overall), as compared to that they serve to browsers.
   In some cases, a site might wish to augment the information that they
   provide to a trusted bot.  Conversely, a site might wish to reduce or
   modify the information that they provide to a bot that they do not
   trust.

   Current practice is difficult to ascertain, but anecdotal evidence
   suggests that the latter case is more common than the former.  For
   example, some sites do not wish for information that they consider to
   be commercially sensitive -- e.g., prices -- to be available to bots.
   In both cases, IP addresses and similar heuristics are used.

   In most cases, this use requires identifying a specific bot and
   associating it with a real-world entity (although there are
   exceptions, such as sites which want to treat all bots equally, or
   cases where it's possible to group bots without identifying specific
   ones).

   This use case is likely to be controversial in cases where the
   modifications are not consensual.  Some espouse a site's right to
   control its own speech depending upon the audience it is speaking to,
   whereas others are concerned by the lack of transparency that might
   result -- particularly from powerful sites.  Note, however, that a
   bot that cannot be distinguished from a typical browser is still
   likely to be able to operate for such purposes.

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2.4.  Auditing Bot Behaviour

   Some sites may wish to understand how bots use them in detail.  In
   particular, they might want to verify that a bot adheres to the
   preferences stated in robots.txt, or that they conform to some other
   protocol.  They might also wish to have reliable metrics for how a
   bot behaves in terms of number of requests, timing of requests, and
   so forth to ascertain the bot's behaviour; this information might
   feed into other use cases, or be used independently.

   Currently, this use case is met through use of heuristics of
   information like IP address.  It does not necessarily require
   identifying a specific bot or associating it with a real-world
   entity, but some (many?) of the downstream uses of the audit data
   may.

   This use case does not appear controversial, because bots being
   accountable for their behaviour is broadly seen as a reasonable goal.

2.5.  Classifying Traffic

   Many sites make efforts to understand how browsers interact with
   them, so as to improve their services.  This might be at the
   connection level (e.g., HTTP, TCP, and QUIC statistics), or it might
   be gathered in-browser (Real User Monitoring or RUM).

   When doing so, it is important for them to be able to distinguish
   between their target audience (people using browsers) and bots; if
   they cannot, the bot traffic will make the insights they gain less
   useful (or even useless).

   Currently, sites that perform such tasks use a variety of heuristics
   to identify and exclude bots from such measures.  This is only
   partially effective; bots are increasingly difficult to classify,
   particularly as using 'headless browsers' becomes a norm for
   crawlers.

   This use case does not require identifying specific bots or
   associating them with real-world entities unless finer granularity of
   classification than "bot vs not" is desired.  However, sites that
   wish to exclude non-human clients from their measurements would still
   need to use heuristics for bots that do not comply with the norm.

   Addressing this use case does not appear to be controversial, because
   an understanding of the nature of traffic that a site receives is
   important to its operation (provided that no personal information is
   involved and no tracking capability is introduced).

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2.6.  Authenticating Site Services

   Many sites use third-party tools to analyse, monitor, and provide
   their services.  For example, health check services allow sites to
   understand their uptimes and receive notifications when there is a
   problem.  Content Delivery Networks need to identify themselves to
   back-end origin servers.

   Currently, such services use a variety of means of authentication,
   including IP address allow lists, "magic" header fields, and ad hoc
   use of other existing mechanisms.

   Site services often have higher requirements for reliability and
   security.  A site might not wish to grant access to a vulnerability
   scanner solely based upon its IP address, for example.  Likewise, a
   health check needs to reliably bypass Web Application Firewalls to
   perform its function.

   This use case requires bot identity to be tied to authentication.

   Addressing this use case does not appear to be controversial.
   However, it is not clear whether these use cases are within the scope
   of the Working Group's charter.

3.  Bot Use Cases

   This section explores use cases that Bots might have for being
   authenticated by sites, focusing on improvements over current
   mechanisms that sites use.

3.1.  IP Address Mobility

   User-Agent headers can be descriptive, but are also trivially
   spoofed.  As a result, most bots are associated most strongly with
   the IP addresses they use.

   Bots that do not fully control the IP addresses they use (e.g., those
   using cloud or other hosting infrastructure) are disadvantaged: if
   they need to change the addresses they use (e.g., due to operational
   issues, economic incentives, or changes by their provider), they lose
   any reputation built and effectively start from scratch.

   As a result, long-term stability of the IP address is necessary to
   build a reputation for that IP address.  Sites often use static allow
   and block lists of IP addresses, so updating them is painful.

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   Identifying a bot using a factor other than IP address would decouple
   its reputation from the infrastructure identifier -- its IP address
   -- and allow greater mobility, levelling the playing field for bots
   that do not fully control their infrastructure.

3.2.  Sharing IP Addresses

   Similarly, bots that share an IP address with other processes --
   either simultaneously or over time -- are disadvantaged because their
   reputation with sites might be affected by other uses of the IP
   address.  Unless they have rigid control of all requests emitted from
   that IP address over a long period of time, that identifier might be
   added to block lists.

   Identifying a bot using a factor other than IP address would allow
   sites to discriminate between different uses of that identifier.
   This would allow bots to operate without a dedicated IP address,
   further levelling the playing field for small bots.

3.3.  Robots.txt Alignment

   The robots.txt format identifies bots by their User-Agent string, but
   this is easily spoofable on the wire.  As a result, a bot might be
   punished by sites that block that identifier based upon fraudulent
   use.

   Identifying a bot in a more reliable fashion in robots.txt would
   avoid this misattribution.

3.4.  Conveying Contextual Information

   Bots have an incentive to be transparent about their operation, so as
   to encourage sites to allow their operation.  Although there are ad
   hoc mechanisms for doing this (e.g., a link to HTML in the User-Agent
   string), a standard, machine-readable means of conveying
   authenticated information about a bot's operation could lower
   barriers to conveying this information.

4.  Next Steps

   This section suggests questions for further investigation and
   discussion.

   1.  What are the qualitative differences between current practice
       (e.g. ad hoc blocking by IP address) and proposals for
       authentication of bots?

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   2.  User authentication is widespread and standards-supported on the
       Web; what makes bot authentication different?

   3.  What levers do we have to mitigate the harms associated with an
       emerging default of requiring authentication for bots?  Does
       authentication enhance or confound such efforts (as opposed to IP
       address blocking)?

   4.  Would an authentication scheme that does not allow association
       with real-world entities provide enough value to meet interesting
       use cases?  If so, would the charter prohibition on "[t]racking
       or assigning reputation to particular bots" need to change?

   5.  What is the threshold for being considered a bot?  E.g., is
       request rate important?  Associating with a specific human user
       in time and/or space?

   6.  Are the resource requirements for authentication proposals
       reasonable for these use cases for all types of sites?  At IETF
       124, it was asserted that it would disproportionately advantage
       already well-resourced entities.

   7.  What use cases should the group address and not address?  Why?

   8.  Are there alternative approaches to addressing some or all of
       these use cases?  What properties do they have?

5.  IANA Considerations

   This draft has no actions for IANA.

6.  Security Considerations

   Undoubtedly there are security considerations to any authentication
   protocol, but they will be encountered and dealt with later than
   what's in scope for this draft.

Appendix A.  Bot Differences

   This section enumerates some of the ways that bots can differ.

A.1.  Scope

   Bots have different scopes of activity:

   *  Some crawl the entire Web

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   *  Some target a specific subset of the Web (e.g., by geography,
      language, industry)

   *  Some target specific sites or resources on sites (e.g., link
      checkers, linters)

A.2.  Relationship

   Bots have different relationships with sites:

   *  Some actively attempt to appear as Web browsers, so as to have the
      same relationship as an end user

   *  Some do not hide their nature as bots but do not have any pre-
      existing relationship with the site

   *  Some are implicitly or explicitly authorised by the site (e.g.,
      through an advertised API)

   *  Some have a pre-existing relationship with the site (e.g.,
      monitoring and other site services)

A.3.  Reputation

   Bots have different reputations in the larger community, which can
   change how they are perceived by sites:

   *  Some are well and widely-known (e.g., search engine crawlers,
      archivers)

   *  Some are relatively unknown (e.g., due to low traffic or recent
      introduction)

   *  Some are purposefully anonymous (e.g., price checkers, most
      malicious bots)

A.4.  Agency

   Bots act with different relationships to their operator(s):

   *  Some are explicitly and exclusively associated with an end user
      (e.g., "agentic" bots)

   *  Some are acting on behalf of a group of end users

   *  Some are acting on behalf of another entity (e.g., corporation,
      government, civil society organisation)

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   *  Some serve multiple constituencies

   Portraying "bot vs. human" is likely an unhelpful binary.

Author's Address

   Mark Nottingham
   Melbourne
   Australia
   Email: mnot@mnot.net
   URI:   https://www.mnot.net/

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