]> Palo Alto Networks

joe@salowey.net

Zscaler

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Applications and Real-Time Workload Identity in Multi System Environments workload identity The WIMSE architecture defines authentication and authorization for software workloads in a variety of runtime environments, from the most basic ones to complex multi-service, multi-cloud, multi-tenant deployments. This document profiles workload authentication based on X.509 Workload Identity Certificates using mutual TLS (mTLS). 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 defines authentication and authorization in the context of interaction between two workloads. This is the core component of the WIMSE architecture . This document focuses on using X.509 Workload Identity Certificates as defined in to authenticate the communication between workloads using TLS. The use of TLS for authentication is widely deployed, however it may not be applicable to all environments. For example, some deployments may lack the Public Key Infrastructure (PKI) necessary to manage certificates or inter-service communication consists of multiple separate TLS hops. For these cases, other options based on Workload Identity Tokens (WIT) as defined in may be more appropriate since they are not based on X.509 certificates and are communicated at the application layer rather than the transport layer.

Deployment Architecture and Message Flow Refer to for the deployment architecture which is common to all authentication mechanisms.

Conventions and Definitions This document uses the terminology defined in . The terms "Workload Identifier" and "trust domain" are defined in , and "Workload Identity Certificate" is defined in . 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.

Using Mutual TLS for Workload-to-Workload Authentication As noted in the introduction, for many deployments, transport-level protection of application traffic using TLS is ideal. This document describes using WIMSE certificates to authenticate a TLS connection. In the case of mutual TLS either the client or the server or both client and server may present WIMSE certificates.

The Workload Identity Certificate Workload Identity Certificates are X.509 certificates that carry Workload Identifiers as described in .

Workload Identity Certificate Validation Workload Identity Certificates may be used to authenticate both the server and client side of the connection. When validating a Workload Identity Certificate, the relying party MUST use a locally configured mapping from trust domains to trust anchors, provisioned as described in . The peer's certificate MUST be rejected unless its certification path validates to a trust anchor configured for the trust domain in its Workload Identifier. The Workload Identifier MUST NOT be treated as authenticated until this validation succeeds. The relying party MUST perform certification path validation in accordance with . Workloads acting as TLS clients or servers MUST validate that the trust domain portion of the Workload Identifier in the Workload Identity Certificate matches the expected trust domain for the other side of the connection. Certificate revocation status MUST be determined as specified in . The mechanism used to determine that status is deployment-specific and may use CRLs, OCSP, or out-of-band information. Servers wishing to use the Workload Identity Certificate for authorizing the client MUST require client certificate authentication in the TLS handshake. Other methods of post handshake authentication are not specified by this document. Workload Identity Certificates used by TLS servers SHOULD have the id-kp-serverAuth extended key usage () field set and Workload Identity Certificates used by TLS clients SHOULD have the id-kp-clientAuth extended key usage field set. A certificate that is used for both client and server connections may have both fields set. This specification does not make any other requirements beyond and on the contents of Workload Identity Certificates or on the certification authorities that issue workload certificates.

Server Name Validation A WIMSE server intended to be accessed using a DNS hostname SHOULD present a certificate containing a matching DNS Subject Alternative Name (DNS-ID). A WIMSE client connecting to a server using a DNS hostname MUST perform standard TLS server identity validation as specified in . When connecting to a server based on its DNS hostname, the client MUST reject the connection if the server's certificate does not contain a matching DNS-ID, even if Workload Identifier validation succeeds. A WIMSE client that expects to connect to a server with a WIMSE certificate MUST validate that the WIMSE identifier of the server is appropriate for the server it is attempting to connect. Since the structure of a WIMSE identifier is deployment specific the validation is deployment specific, but the client MUST at least verify that the trust domain of the WIMSE identifier matches the trust domain of the server it intends to connect to. Some deployments may require the identification of servers by their WIMSE identifier. In such cases, the client MUST be configured with sufficient information to determine the expected Workload Identifier of the server and the client MUST validate the Workload Identifier in the server's certificate against that expectation before accepting the connection. The Workload Identifier can be used for additional workload-specific authorization and policy decisions. Connecting directly to an IP address does not require an IP address subjectAltName when the client authenticates the server using its expected Workload Identifier. If the client additionally requires authentication of the server's IP address, it MUST validate a matching iPAddress subjectAltName (IP-ID) as specified in . If no matching IP-ID is present, the client MUST reject the connection, even if Workload Identifier validation succeeds. The authority part of a URI that is a Workload Identifier is NOT treated as a hostname as otherwise specified in , but rather as a trust domain as specified in . The server identity is encoded in the path portion of the Workload Identifier in a deployment-specific way. Validation of the workload identity may consist of an exact match of the trust domain and path, or may follow deployment-specific rules. The path portion of the Workload Identifier MUST always be interpreted within the context of the trust domain. In most cases it is preferable to validate the entire Workload Identifier; see for additional implementation guidance.

Client Authorization Using the Workload Identity The server application retrieves the Workload Identifier from the client certificate's URI subjectAltName (see ), which in turn is obtained from the TLS layer. The certificate MUST contain exactly one URI subjectAltName carrying a Workload Identifier, as specified in . Certificates containing zero or multiple such entries MUST be rejected. The identifier is used in authorization, accounting and auditing. For example, the full Workload Identifier may be matched against ACLs to authorize actions requested by the peer and the identifier may be included in log messages to associate actions with the client workload for audit purposes. A deployment may specify other authorization policies based on the specific details of how the Workload Identifier is constructed. The path portion of the Workload Identifier MUST always be considered in the scope of the trust domain of the Workload Identifier. See for additional security implications of Workload Identifiers.

IANA Considerations This document does not include any IANA considerations.

Security Considerations

Certificate and Identity Validation This document relies on the security properties of TLS , PKIX path validation (), and Workload Identity Certificate validation as described in . Implementations MUST validate the peer certificate chain, the applicable extended key usage (if present), and the Workload Identifier according to the rules in this document before using the authenticated identity for authorization decisions. Workload Identifiers are meaningful only within the scope of their trust domain. Authorization policies MUST NOT evaluate only the path or other sub-components of a Workload Identifier without also considering the trust domain and the trust anchor used to validate the certificate. Failure to bind the Workload Identifier to the proper trust domain and its configured trust anchor can allow one trust domain to impersonate workloads from another domain. When a client identifies a server by a DNS hostname, clients MUST authenticate the server using standard TLS DNS hostname validation as specified in . When a client expects to connect to a server identified by a WIMSE identity then it MUST validate that the WIMSE identifier of the server according to domain specific policy as defined in . Only deployments that do not rely on DNS-based server identification should authenticate the server solely using its workload identity. Accepting any certificate issued by a trusted workload CA without validating that it represents the intended server workload would allow mis-issued or otherwise valid certificates for other workloads to be used for impersonation. Client authentication is based on the Workload Identity Certificate presented by the TLS client. A server performing mTLS authentication MUST validate the client certificate chain, the associated trust domain, and the Workload Identifier before using that identity for authorization, accounting, or auditing. Accepting any valid client certificate from a trusted CA without checking whether the authenticated workload is authorized for the requested action can allow unintended workloads to gain access.

Certificate and Private Key Management Workload Identity Certificates are often issued to dynamic or short-lived workloads. Deployments SHOULD use certificate lifetimes that are appropriate for the workload environment and SHOULD provide timely revocation or replacement mechanisms when workload identity, authorization, or runtime state changes. Long-lived certificates increase the impact of private key compromise and stale authorization decisions. Compromise of the private key corresponding to a trust anchor can enable impersonation for as long as that anchor remains trusted, regardless of leaf certificate lifetimes. Trust-anchor provisioning and lifecycle considerations, including lifetime and rotation, are discussed in and . Private keys associated with Workload Identity Certificates MUST be protected against disclosure and unauthorized use. In particular, deployments MUST NOT share private keys across unrelated workload instances. Where possible, private keys SHOULD be generated and held in the workload runtime environment or a dedicated key protection mechanism, rather than distributed over the network.

TLS Termination at Intermediaries This document specifies authentication at the TLS layer. If application traffic traverses intermediaries, gateways, service meshes, or other middleboxes that terminate and re-establish TLS, the application endpoint might not be directly authenticated to the peer workload. In such deployments, authorization decisions need to account for where TLS is terminated and whether the authenticated certificate represents the peer workload, an intermediary, or another delegated entity. Where end-to-end workload authentication context is required across such boundaries, deployments SHOULD use an application-layer WIMSE authentication mechanism, such as or , in addition to TLS-layer server authentication.

Application-Layer Identity Assertions Authorization decisions based on workload identity MUST be made using the authenticated identity obtained from the validated certificate, not from unauthenticated application-layer metadata such as HTTP headers. Application-layer identity assertions can be useful for logging or context, but they MUST NOT override the identity established by mutual TLS unless protected and authorized by another mechanism.

Privacy Considerations Client certificate authentication exposes the client workload identity to the TLS server during the handshake. Deployments should consider whether disclosure of Workload Identifiers to servers, intermediaries, or logs is acceptable for their threat model. Workload Identifiers included in certificates and audit records should avoid embedding unnecessary sensitive information.

References Normative References Ping Identity CyberArk Defakto Security Intuit Zscaler 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 credentials that workloads use to represent their identity. They can be used in various protocols to authenticate workloads to each other. To use these credentials, workloads must provide proof of possession of the associated private key material, which is covered in other documents. This document focuses on the credentials alone, independent of the proof-of- possession mechanism. Zscaler Palo Alto Networks This document defines a canonical identifier for workloads, referred to as the Workload Identifier. A Workload Identifier is a URI that uniquely identifies a workload within the context of a specific trust domain. This identifier can be embedded in Workload Identity Credentials, including X.509 certificates and JWT-based tokens, to support authentication, authorization, and policy enforcement across diverse systems. The Workload Identifier format ensures interoperability, facilitates secure identity federation, and enables consistent identity semantics. 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. This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] Many application technologies enable secure communication between two entities by means of Transport Layer Security (TLS) with Internet Public Key Infrastructure using X.509 (PKIX) certificates. This document specifies procedures for representing and verifying the identity of application services in such interactions. This document obsoletes RFC 6125. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document obsoletes RFC 8446, which specified TLS 1.3. This document obsoletes RFC 5246 (specifying TLS 1.2) and RFCs 5077, 6961, 7627, and 8422, all of which pertain to TLS 1.2 or earlier, and updates RFCs 5705 and 6066. This document also specifies new requirements for TLS 1.2 implementations. Informative References Palo Alto Networks Zscaler University of the Bundeswehr Munich 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 software executing for a specific purpose, potentially comprising one or more running instances. This document discusses an architecture for designing and standardizing protocols and payloads for conveying workload identity and security context information. Palo Alto Networks Independent The WIMSE architecture defines authentication and authorization for software workloads in a variety of runtime environments, from the most basic ones to complex multi-service, multi-cloud, multi-tenant deployments. This document defines one of the mechanisms to provide workload authentication, using HTTP Signatures. While only applicable to HTTP traffic, the protocol provides end-to-end protection of requests (and optionally, responses), even when service traffic is not end-to-end encrypted, that is, when TLS proxies and load balancers are used. Authentication is based on the Workload Identity Token (WIT). Ping Identity Defakto Security The WIMSE architecture defines authentication and authorization for software workloads in a variety of runtime environments, from basic deployments to complex multi-service, multi-cloud, multi-tenant systems. This document specifies the Workload Proof Token (WPT), a mechanism for workloads to prove possession of the private key associated with a Workload Identity Token (WIT). The WPT is a signed JWT that binds the workload's authentication to a specific HTTP request, providing application-layer proof of possession for workload-to-workload communication. This specification is designed to work alongside the WIT credential format defined in draft-ietf- wimse-workload-creds and can be combined with other WIMSE protocols in multi-hop call chains.

Document History RFC Editor: please remove before publication.

draft-ietf-wimse-mutual-tls-03

• Editorial: consistent capitalization of the defined terms "Workload Identifier" and "Workload Identity Certificate".

draft-ietf-wimse-mutual-tls-02

• Improved Server Name Validation section

draft-ietf-wimse-mutual-tls-01

• Added security considerations

draft-ietf-wimse-mutual-tls-00

• Initial version, extracted from the draft-ietf-wimse-s2s-protocol-07 S2s draft with minimal edits.
• added security consideration for Server Name Validation

Acknowledgments We thank Yaron Sheffer, Arndt Schwenkschuster, Brian Campbell, and Daniel Feldman for their contributions to earlier versions of this document.