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Introduction to SPIFFE

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SPIFFE (Secure Production Identity Framework For Everyone) is a set of standards for securely identifying workloads.

SPIFFE sets out:

  • A format for uniquely specifying an identity called SPIFFE ID.
  • Standards for encoding the SPIFFE ID into verifiable documents which are called SVIDs (SPIFFE Verifiable Identity Document), and which come in a JWT and X.509 format.
  • Processes that workloads should use to validate a received SVID.
  • A set of APIs that workloads can use to request SVIDS, the Workload API.

The open nature and popularity of SPIFFE make it well-suited as the foundation of a full workload identity implementation. It is supported as an identity provider by a number of popular tools (such as Linkerd and Istio) and off-the-shelf SDKs exist for implementing SPIFFE directly into your own services.

It's important to recognize that SPIFFE does not specify how to use SPIFFE IDs for authorization. This gives a high level of flexibility, allowing you to implement authorization in a way that suits you.

SPIFFE IDs and trust domains

The basis of identity in SPIFFE is the SPIFFE ID. This is a unique string that identifies a workload. The SPIFFE ID is formatted as a URI with a scheme of spiffe and contains a trust domain and a workload identifier.

The trust domain is the "root of trust" for your workload identities. Workloads within the trust domain are issued identities by authorities within the trust domain, and using the root keys of the trust domain, it is possible to validate these identities. The trust domain is encoded as the host within the URI. For Teleport Workload Identity, the trust domain is your Teleport cluster, and this is represented by the name configured for the cluster, e.g example.teleport.sh.

The workload identifier is encoded in the URI as the path. This should be a string that identifies your workload within the trust domain. What you include within this path is up to you and your application's requirements. Typically, the hierarchical nature of the path is leveraged. For example, you had the service foo operating in the europe region, you may wish to represent this as: /region/europe/svc/foo.

Together, this produces a SPIFFE ID that looks like:

spiffe://example.teleport.sh/region/europe/svc/foo

Secure Verifiable Identity Documents (SVIDs)

The SPIFFE ID may be a unique identifier for a workload, but provides no way for a workload to verifiably prove its identity. This is where the Secure Verifiable Identity Documents (SVIDs) come in.

The SVID is a document that encodes the SPIFFE ID and a cryptographic proof which allows the SVID to be verified as issued by a trusted authority.

SPIFFE sets out two formats for SVIDs:

  • X.509-SVID: These are X.509 certificates that include the SPIFFE ID encoded in the URI SAN field. This certificate is then signed by a trusted authority within the trust domain.
  • JWT-SVID: These are JWT tokens that include the SPIFFE ID as the sub claim. These are signed by a trusted authority within the trust domain.

The data needed by a workload to verify a SVID is known as the trust bundle. This is a set of certificates belonging to the trusted authorities within the trust domain.

Workload API

The Workload API is a standardized gRPC API that workloads should use to request SVIDs and trust bundles from a SPIFFE identity provider. The Workload API server also handles automatically renewing the credentials for subscribed workloads.

The Workload API is usually exposed by an agent that is installed on the same host as the workloads and is accessed using a unix socket rather than a TCP endpoint. It can perform basic authentication and authorization of the workload before issuing SVIDs. This is known as Workload Attestation.

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