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Applications and Real-Time Workload Identity in Multi System Environments workload identity This document defines an HTTP Message Signatures-based profile for workload-to-workload authentication within the WIMSE (Workload Identity in Multi System Environments) architecture. This profile uses the Workload Identity Token (WIT) combined with HTTP Message Signatures to provide cryptographic proof of possession and message integrity protection. The profile leverages RFC 9421 to sign HTTP requests and optionally responses, ensuring that workloads can authenticate each other and verify message integrity at the application level, particularly in environments where end-to-end TLS is not feasible due to middleboxes or other infrastructure constraints. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Workload Identity in Multi System Environments Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction This document specifies an HTTP Message Signatures-based authentication profile for workload-to-workload communication as part of the WIMSE architecture defined in . This profile provides a standardized approach for workloads to authenticate each other and protect message integrity at the application level. In many modern deployment environments, particularly in containerized and cloud-native architectures, workloads cannot rely on end-to-end TLS for security due to the presence of load balancers, API gateways, service meshes, and other intermediary systems. These middleboxes often terminate TLS connections, requiring application-level protection mechanisms to ensure workload authentication and message integrity. This profile builds upon the base WIMSE workload-to-workload protocol and specifies the use of HTTP Message Signatures as the proof of possession mechanism. The approach combines:

1. The Workload Identity Token (WIT) - a JWT that establishes the workload's identity and binds it to a cryptographic key
2. HTTP Message Signatures - providing cryptographic proof that the sender possesses the private key corresponding to the public key in the WIT
3. Message integrity protection - ensuring that critical parts of HTTP requests and responses have not been modified

This profile is particularly suitable for deployments that require strong message integrity guarantees and the ability to sign both requests and responses. It provides protection against message tampering by intermediaries while allowing for the flexibility needed in complex multi-tier architectures. The profile defines specific requirements for which HTTP message components must be signed, signature parameters that must be included, and validation procedures that recipients must follow. It is designed to be interoperable with other WIMSE authentication profiles, allowing different workload pairs within the same call chain to use different authentication methods as appropriate for their deployment environment.

Conventions and Definitions All terminology in this document follows . 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.

Authentication Based on HTTP Message Signatures This option uses the Workload Identity Token (WIT) as defined in Section 3.1 "The Workload Identity Token" of and the private key associated with its public key, to sign the request and optionally, the response. See Section 4 "Security Considerations" of for security considerations. This section defines a profile of the Message Signatures specification . The request is signed as per . The following derived components MUST be signed:

• @method
• @request-target

In addition, the following request headers MUST be signed when they exist:

• Content-Type
• Content-Digest
• Authorization
• Txn-Token
• Workload-Identity-Token

If the response is signed, the following components MUST be signed:

• @status
• @method;req
• @request-target;req
• Content-Type if it exists
• Content-Digest if it exists
• Workload-Identity-Token

To ensure the message is fully integrity-protected, if the request or response includes a message body, the sender MUST include (and the receiver MUST verify) a Content-Digest header. For both requests and responses, the following signature parameters MUST be included:

• created
• expires - expiration MUST be short, e.g. on the order of minutes. The WIMSE architecture will provide separate mechanisms in support of long-lived compute processes.
• nonce
• tag - the value for implementations of this specification is wimse-workload-to-workload

The following signature parameters in the Signature-Input header MUST NOT be used:

• keyid - The signing key is sent along with the message in the WIT. Additionally specifying the key identity would add confusion.
• alg - The signature algorithm is specified in the jwk section of the cnf claim in the WIT as defined in Section 3.1 "The Workload Identity Token" of . See Sec. 3.3.7 of for details.

It is RECOMMENDED to include only one signature with the HTTP message. If multiple ones are included, then the signature label included in both the Signature-Input and Signature headers SHOULD be wimse. A sender MUST ensure that each nonce it generates is unique, at least among messages sent to the same recipient. To detect message replays, a recipient SHOULD reject a message (request or response) if a nonce generated by a certain peer is seen more than once. Implementors need to be aware that the WIT is extracted from the message before the message signature is validated. Recipients of signed HTTP messages MUST validate the signature and content of the WIT before validating the HTTP message signature. They MUST ensure that the message is not processed further before it has been fully validated. Either client or server MAY send an Accept-Signature header, but is not required to do so. When this header is sent, it MUST include the header components listed above. Following is a non-normative example of a signed request and a signed response, where the caller is using the keys specified in Section 3.1 "The Workload Identity Token" of .

Signed Request

Assuming that the workload being called has the following keypair:

Callee Private Key

A signed response would be:

Signed Response

Error Conditions Errors may occur during the processing of the message signature or WPT. If the signature verification fails for any reason, such as an invalid signature, an expired validity time window, or a malformed data structure, an error is returned. Typically, this will be in response to an API call, so an HTTP status code such as 400 (Bad Request) is appropriate. This response could include more details as per , such as an indicator that the wrong key material or algorithm was used. The use of HTTP status code 401 is NOT RECOMMENDED for this purpose because it requires a WWW-Authenticate with acceptable http auth mechanisms in the error response and an associated Authorization header in the subsequent request. The use of these headers for the WIT or WPT is not compatible with this specification.

Coexistence with JWT Bearer Tokens The WIT and WPT define new HTTP headers. They can therefore be presented along with existing headers used for JWT bearer tokens. This property allows for transition from mechanisms using identity tokens based on bearer JWTs to proof of possession based WITs. A workload may implement a policy that accepts both bearer tokens and WITs during a transition period. This policy may be configurable per-caller to allow the workload to reject bearer tokens from callers that support WITs. Once a deployment fully supports WITs, then the use of bearer tokens for identity can be disabled through policy. Implementations should be careful when implementing such a transition strategy, since the decision which token to prefer is made when the caller's identity has still not been authenticated, and needs to be revalidated following the authentication step. The WIT can also coexist with tokens used to establish security context, such as transaction tokens . In this case a workload's authorization policy may take into account both the sending workload's identity and the information in the context token. For example, the identity in the WIT may be used to establish which API calls can be made and information in the context token may be used to determine which specific resources can be accessed.

Security Considerations

Workload Identity Token and Proof of Possession The Workload Identity Token (WIT) is bound to a secret cryptographic key and is always presented with a proof of possession as described in Section 3.1 "The Workload Identity Token" of . The WIT is a general purpose token that can be presented in multiple contexts. The WIT and its PoP are only used in the application-level options, and both are not used in MTLS. The WIT MUST NOT be used as a bearer token. While this helps reduce the sensitivity of the token it is still possible that a token and its proof of possession may be captured and replayed within the PoP's lifetime. The following are some mitigations for the capture and reuse of the proof of possession (PoP):

• Preventing Eavesdropping and Interception with TLS

An attacker observing or intercepting the communication channel can view the token and its proof of possession and attempt to replay it to gain an advantage. In order to prevent this the token and proof of possession MUST be sent over a secure, server authenticated TLS connection unless a secure channel is provided by some other mechanisms. Host name validation according to Section 3.3.1 "Server Name Validation" of MUST be performed by the client.

• Limiting Proof of Possession Lifespan

The proof of possession MUST be time limited. A PoP should only be valid over the time necessary for it to be successfully used for the purpose it is needed. This will typically be on the order of minutes. PoPs received outside their validity time MUST be rejected.

• Limiting Proof of Possession Scope

In order to reduce the risk of theft and replay the PoP should have a limited scope. For example, a PoP may be targeted for use with a specific workload and even a specific transaction to reduce the impact of a stolen PoP. In some cases a workload may wish to reuse a PoP for a period of time or have it accepted by multiple target workloads. A careful analysis is warranted to understand the impacts to the system if a PoP is disclosed allowing it to be presented by an attacker along with a captured WIT.

• Replay Protection

A proof of possession includes the jti claim that MUST uniquely identify it, within the scope of a particular sender. This claim SHOULD be used by the receiver to perform basic replay protection against tokens it has already seen. Depending upon the design of the system it may be difficult to synchronize the replay cache across all token validators. If an attacker can somehow influence the identity of the validator (e.g. which cluster member receives the message) then replay protection would not be effective.

• Binding to TLS Endpoint

The POP MAY be bound to a transport layer sender such as the client identity of a TLS session or TLS channel binding parameters. The mechanisms for binding are outside the scope of this specification.

Middle Boxes In some deployments the Workload Identity Token and proof of possession may pass through multiple systems. The communication between the systems is over TLS, but the token and PoP are available in the clear at each intermediary. While the intermediary cannot modify the token or the information within the PoP they can attempt to capture and replay the token or modify the data not protected by the PoP. Mitigations listed in Section 4.3 "Middle Boxes" of can be used to provide some protection from middle boxes. However we note that the DPoP-inspired solution does not protect major portions of the request and response and therefore does not provide protection from an actively malicious middle box. Deployments should perform analysis on their situation to determine if it is appropriate to trust and allow traffic to pass through a middle box.

Privacy Considerations Privacy considerations for this specification are the same as those described in Section 4.4 "Privacy Considerations" of .

IANA Considerations None

References Normative References 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] JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification. A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data structure that represents a cryptographic key. This specification also defines a JWK Set JSON data structure that represents a set of JWKs. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries established by that specification. This specification registers cryptographic algorithms and identifiers to be used with the JSON Web Signature (JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK) specifications. It defines several IANA registries for these identifiers. JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted. This specification describes how to declare in a JSON Web Token (JWT) that the presenter of the JWT possesses a particular proof-of- possession key and how the recipient can cryptographically confirm proof of possession of the key by the presenter. Being able to prove possession of a key is also sometimes described as the presenter being a holder-of-key. JSON Web Tokens, also known as JWTs, are URL-safe JSON-based security tokens that contain a set of claims that can be signed and/or encrypted. JWTs are being widely used and deployed as a simple security token format in numerous protocols and applications, both in the area of digital identity and in other application areas. This Best Current Practices document updates RFC 7519 to provide actionable guidance leading to secure implementation and deployment of JWTs. The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. This document describes a mechanism for creating, encoding, and verifying digital signatures or message authentication codes over components of an HTTP message. This mechanism supports use cases where the full HTTP message may not be known to the signer and where the message may be transformed (e.g., by intermediaries) before reaching the verifier. This document also describes a means for requesting that a signature be applied to a subsequent HTTP message in an ongoing HTTP exchange. 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. 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 IANA IANA IANA IANA IANA This document defines a "problem detail" to carry machine-readable details of errors in HTTP response content to avoid the need to define new error response formats for HTTP APIs. This document obsoletes RFC 7807. CyberArk Zscaler University of Applied Sciences Bonn-Rhein-Sieg The increasing prevalence of cloud computing and micro service architectures has led to the rise of complex software functions being built and deployed as workloads, where a workload is defined as a running instance of software executing for a specific purpose. This document discusses an architecture for designing and standardizing protocols and payloads for conveying workload identity and security context information. Ping Identity CyberArk SPIRL Intuit The WIMSE architecture defines authentication and authorization for software workloads in a variety of runtime environments, from the most basic ones up to complex multi-service, multi-cloud, multi- tenant deployments. This document defines the simplest, atomic unit of this architecture: the protocol between two workloads that need to verify each other's identity in order to communicate securely. The scope of this protocol is a single HTTP request-and-response pair. To address the needs of different setups, we propose two protocols, one at the application level and one that makes use of trusted TLS transport. These two protocols are compatible, in the sense that a single call chain can have some calls use one protocol and some use the other. Workload A can call Workload B with mutual TLS authentication, while the next call from Workload B to Workload C would be authenticated at the application level. SGNL Practical Identity LLC SPIRL Transaction Tokens (Txn-Tokens) are designed to maintain and propagate user identity and authorization context across workloads within a trusted domain during the processing of external programmatic requests, such as API calls. They ensure that this context is preserved throughout the call chain, even when new transactions are initiated internally, thereby enhancing security and consistency in complex, multi-service architectures.

Document History RFC Editor: please remove before publication.

draft-schwenkschuster-s2s-http-sig-00 Initial clone from original draft-ietf-wimse-s2s-06 which contained both, Workload Proof Token and HTTP Message Signature proof of possession mechanisms.

Acknowledgments The authors would like to thank Pieter Kasselman for his detailed comments. We thank Daniel Feldman for his contributions to earlier versions of this document.