Simplify SCEP provisioner context handling

authority/authority.go

@@ -858,8 +858,8 @@ func (a *Authority) IsRevoked(sn string) (bool, error) {
 	return a.db.IsRevoked(sn)
 }
 
-// requiresSCEPService iterates over the configured provisioners
-// and determines if one of them is a SCEP provisioner.
+// requiresSCEP iterates over the configured provisioners
+// and determines if at least one of them is a SCEP provisioner.
 func (a *Authority) requiresSCEP() bool {
 	for _, p := range a.config.AuthorityConfig.Provisioners {
 		if p.GetType() == provisioner.TypeSCEP {

scep/api/api.go

@@ -221,7 +221,7 @@ func lookupProvisioner(next http.HandlerFunc) http.HandlerFunc {
 			return
 		}
 
-		ctx = context.WithValue(ctx, scep.ProvisionerContextKey, scep.Provisioner(prov))
+		ctx = scep.NewProvisionerContext(ctx, scep.Provisioner(prov))
 		next(w, r.WithContext(ctx))
 	}
 }

scep/authority.go

@@ -136,10 +136,7 @@ func (a *Authority) LoadProvisionerByName(name string) (provisioner.Interface, e
 // Using an RA does not seem to exist in https://tools.ietf.org/html/rfc8894, but is mentioned in
 // https://tools.ietf.org/id/draft-nourse-scep-21.html.
 func (a *Authority) GetCACertificates(ctx context.Context) (certs []*x509.Certificate, err error) {
-	p, err := provisionerFromContext(ctx)
-	if err != nil {
-		return
-	}
+	p := provisionerFromContext(ctx)
 
 	// if a provisioner specific RSA decrypter is available, it is returned as
 	// the first certificate.
@@ -214,10 +211,7 @@ func (a *Authority) DecryptPKIEnvelope(ctx context.Context, msg *PKIMessage) err
 }
 
 func (a *Authority) selectDecrypter(ctx context.Context) (cert *x509.Certificate, pkey crypto.PrivateKey, err error) {
-	p, err := provisionerFromContext(ctx)
-	if err != nil {
-		return nil, nil, err
-	}
+	p := provisionerFromContext(ctx)
 
 	// return provisioner specific decrypter, if available
 	if cert, pkey = p.GetDecrypter(); cert != nil && pkey != nil {
@@ -239,10 +233,7 @@ func (a *Authority) SignCSR(ctx context.Context, csr *x509.CertificateRequest, m
 	// poll for the status. It seems to be similar as what can happen in ACME, so might want to model
 	// the implementation after the one in the ACME authority. Requires storage, etc.
 
-	p, err := provisionerFromContext(ctx)
-	if err != nil {
-		return nil, err
-	}
+	p := provisionerFromContext(ctx)
 
 	// check if CSRReqMessage has already been decrypted
 	if msg.CSRReqMessage.CSR == nil {
@@ -463,10 +454,7 @@ func (a *Authority) CreateFailureResponse(_ context.Context, _ *x509.Certificate
 
 // GetCACaps returns the CA capabilities
 func (a *Authority) GetCACaps(ctx context.Context) []string {
-	p, err := provisionerFromContext(ctx)
-	if err != nil {
-		return defaultCapabilities
-	}
+	p := provisionerFromContext(ctx)
 
 	caps := p.GetCapabilities()
 	if len(caps) == 0 {
@@ -483,9 +471,6 @@ func (a *Authority) GetCACaps(ctx context.Context) []string {
 }
 
 func (a *Authority) ValidateChallenge(ctx context.Context, challenge, transactionID string) error {
-	p, err := provisionerFromContext(ctx)
-	if err != nil {
-		return err
-	}
+	p := provisionerFromContext(ctx)
 	return p.ValidateChallenge(ctx, challenge, transactionID)
 }

scep/provisioner.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"crypto"
 	"crypto/x509"
-	"errors"
 	"time"
 
 	"github.com/smallstep/certificates/authority/provisioner"
@@ -24,25 +23,20 @@ type Provisioner interface {
 	ValidateChallenge(ctx context.Context, challenge, transactionID string) error
 }
 
-// ContextKey is the key type for storing and searching for SCEP request
-// essentials in the context of a request.
-type ContextKey string
-
-const (
-	// ProvisionerContextKey provisioner key
-	ProvisionerContextKey = ContextKey("provisioner")
-)
+// provisionerKey is the key type for storing and searching a
+// SCEP provisioner in the context.
+type provisionerKey struct{}
 
 // provisionerFromContext searches the context for a SCEP provisioner.
-// Returns the provisioner or an error.
-func provisionerFromContext(ctx context.Context) (Provisioner, error) {
-	val := ctx.Value(ProvisionerContextKey)
-	if val == nil {
-		return nil, errors.New("provisioner expected in request context")
-	}
-	p, ok := val.(Provisioner)
-	if !ok || p == nil {
-		return nil, errors.New("provisioner in context is not a SCEP provisioner")
+// Returns the provisioner or panics if no SCEP provisioner is found.
+func provisionerFromContext(ctx context.Context) Provisioner {
+	p, ok := ctx.Value(provisionerKey{}).(Provisioner)
+	if !ok {
+		panic("SCEP provisioner expected in request context")
 	}
-	return p, nil
+	return p
+}
+
+func NewProvisionerContext(ctx context.Context, p Provisioner) context.Context {
+	return context.WithValue(ctx, provisionerKey{}, p)
 }