Prahran VIC Australia mnot@mnot.net https://www.mnot.net/

General bearer token token scanning This document registers the "secret-token" URI scheme to aid in the identification of authentication tokens.

Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

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Table of Contents

• .  Introduction
  • .  Notational Conventions
• .  The "secret-token" URI Scheme
• .  IANA Considerations
• .  Security Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgements
• Author's Address

Introduction It has become increasingly common to use bearer tokens as an authentication mechanism in various protocols. A bearer token is a security token with the property that any party in possession of the token (a "bearer") can use the token in any way that any other party in possession of it can. Using a bearer token does not require a bearer to prove possession of cryptographic key material (proof-of-possession). Unfortunately, the number of security incidents involving accidental disclosure of these tokens has also increased. For example, we now regularly hear about a developer committing an access token to a public source code repository, either because they didn't realize it was included in the committed code or because they didn't realize the implications of its disclosure. This specification registers the "secret-token" URI scheme to aid prevention of such accidental disclosures. When tokens are easier to unambiguously identify, they can trigger warnings in continuous integration systems or be used in source code repositories themselves. They can also be scanned for separately. For example, if cloud.example.net issues access tokens to its clients for later use, and it does so by formatting them as "secret-token" URIs, tokens that "leak" into places that they don't belong are easier to identify. This could be through a variety of mechanisms; for example, if repo.example.com can be configured to refuse commits containing "secret-token" URIs, it helps its customers avoid accidental disclosures. "secret-token" URIs are intended to aid in identification of generated secrets, like API keys and similar tokens. They are not intended for use in controlled situations where ephemeral tokens are used, such as things like Cross-Site Request Forgery (CSRF) tokens.

Notational Conventions 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. This document uses ABNF . It also uses the pchar rule from .

The "secret-token" URI Scheme The "secret-token" URI scheme identifies a token that is intended to be a secret. secret-token-URI = secret-token-scheme ":" token secret-token-scheme = "secret-token" token = 1*pchar See for a definition of pchar. Disallowed characters -- including non-ASCII characters -- MUST be encoded into UTF-8 and then percent-encoded (). When a token is both generated and presented for authentication, the entire URI MUST be used, without changes. For example, given the URI: secret-token:E92FB7EB-D882-47A4-A265-A0B6135DC842%20foo This (character-for-character, case-sensitive) string will both be issued by the token authority and required for later access. Therefore, if the example above were used as a bearer token in , a client might send: GET /authenticated/stuff HTTP/1.1 Host: www.example.com Authorization: Bearer secret-token:E92FB7EB-D882-47A4-A265-A0B6135DC842%20foo

IANA Considerations This document registers the following value in the "Uniform Resource Identifier (URI) Schemes" registry:

Scheme name:

secret-token

Status:

provisional

Applications/protocols that use this scheme:

none yet

Contact:

iesg@iesg.org

Change Controller:

IESG

References:

RFC 8959

Security Considerations The token ABNF rule allows tokens as small as one character. This is not recommended practice; applications should evaluate their requirements for entropy and issue tokens correspondingly. See for more information. This URI scheme is intended to reduce the incidence of accidental disclosure; it cannot prevent intentional disclosure. If it is difficult to correctly handle secret material, or unclear as to what the appropriate handling is, users might choose to obfuscate their secret tokens in order to evade detection (for example, removing the URI scheme for storage). Mitigating this risk is often beyond the reach of the system using the "secret-token" URI; users can be cautioned against such practices and be provided tools to help.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279. A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Security systems are built on strong cryptographic algorithms that foil pattern analysis attempts. However, the security of these systems is dependent on generating secret quantities for passwords, cryptographic keys, and similar quantities. The use of pseudo-random processes to generate secret quantities can result in pseudo-security. A sophisticated attacker may find it easier to reproduce the environment that produced the secret quantities and to search the resulting small set of possibilities than to locate the quantities in the whole of the potential number space. Choosing random quantities to foil a resourceful and motivated adversary is surprisingly difficult. This document points out many pitfalls in using poor entropy sources or traditional pseudo-random number generation techniques for generating such quantities. It recommends the use of truly random hardware techniques and shows that the existing hardware on many systems can be used for this purpose. It provides suggestions to ameliorate the problem when a hardware solution is not available, and it gives examples of how large such quantities need to be for some applications. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This specification describes how to use bearer tokens in HTTP requests to access OAuth 2.0 protected resources. Any party in possession of a bearer token (a "bearer") can use it to get access to the associated resources (without demonstrating possession of a cryptographic key). To prevent misuse, bearer tokens need to be protected from disclosure in storage and in transport. [STANDARDS-TRACK]

Acknowledgements The definition of bearer tokens is from .

Author's Address

Prahran VIC Australia mnot@mnot.net https://www.mnot.net/