certificates/acme/api/middleware.go
2022-05-02 17:35:35 -07:00

496 lines
15 KiB
Go

package api
import (
"context"
"crypto/rsa"
"errors"
"io"
"net/http"
"net/url"
"strings"
"go.step.sm/crypto/jose"
"go.step.sm/crypto/keyutil"
"github.com/smallstep/certificates/acme"
"github.com/smallstep/certificates/api/render"
"github.com/smallstep/certificates/authority/provisioner"
"github.com/smallstep/certificates/logging"
"github.com/smallstep/nosql"
)
type nextHTTP = func(http.ResponseWriter, *http.Request)
func logNonce(w http.ResponseWriter, nonce string) {
if rl, ok := w.(logging.ResponseLogger); ok {
m := map[string]interface{}{
"nonce": nonce,
}
rl.WithFields(m)
}
}
// addNonce is a middleware that adds a nonce to the response header.
func addNonce(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
db := acme.MustDatabaseFromContext(r.Context())
nonce, err := db.CreateNonce(r.Context())
if err != nil {
render.Error(w, err)
return
}
w.Header().Set("Replay-Nonce", string(nonce))
w.Header().Set("Cache-Control", "no-store")
logNonce(w, string(nonce))
next(w, r)
}
}
// addDirLink is a middleware that adds a 'Link' response reader with the
// directory index url.
func addDirLink(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
linker := acme.MustLinkerFromContext(ctx)
w.Header().Add("Link", link(linker.GetLink(ctx, acme.DirectoryLinkType), "index"))
next(w, r)
}
}
// verifyContentType is a middleware that verifies that content type is
// application/jose+json.
func verifyContentType(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
p, err := provisionerFromContext(r.Context())
if err != nil {
render.Error(w, err)
return
}
u := &url.URL{
Path: acme.GetUnescapedPathSuffix(acme.CertificateLinkType, p.GetName(), ""),
}
var expected []string
if strings.Contains(r.URL.String(), u.EscapedPath()) {
// GET /certificate requests allow a greater range of content types.
expected = []string{"application/jose+json", "application/pkix-cert", "application/pkcs7-mime"}
} else {
// By default every request should have content-type applictaion/jose+json.
expected = []string{"application/jose+json"}
}
ct := r.Header.Get("Content-Type")
for _, e := range expected {
if ct == e {
next(w, r)
return
}
}
render.Error(w, acme.NewError(acme.ErrorMalformedType,
"expected content-type to be in %s, but got %s", expected, ct))
}
}
// parseJWS is a middleware that parses a request body into a JSONWebSignature struct.
func parseJWS(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
body, err := io.ReadAll(r.Body)
if err != nil {
render.Error(w, acme.WrapErrorISE(err, "failed to read request body"))
return
}
jws, err := jose.ParseJWS(string(body))
if err != nil {
render.Error(w, acme.WrapError(acme.ErrorMalformedType, err, "failed to parse JWS from request body"))
return
}
ctx := context.WithValue(r.Context(), jwsContextKey, jws)
next(w, r.WithContext(ctx))
}
}
// validateJWS checks the request body for to verify that it meets ACME
// requirements for a JWS.
//
// The JWS MUST NOT have multiple signatures
// The JWS Unencoded Payload Option [RFC7797] MUST NOT be used
// The JWS Unprotected Header [RFC7515] MUST NOT be used
// The JWS Payload MUST NOT be detached
// The JWS Protected Header MUST include the following fields:
// * “alg” (Algorithm)
// * This field MUST NOT contain “none” or a Message Authentication Code
// (MAC) algorithm (e.g. one in which the algorithm registry description
// mentions MAC/HMAC).
// * “nonce” (defined in Section 6.5)
// * “url” (defined in Section 6.4)
// * Either “jwk” (JSON Web Key) or “kid” (Key ID) as specified below<Paste>
func validateJWS(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
db := acme.MustDatabaseFromContext(ctx)
jws, err := jwsFromContext(ctx)
if err != nil {
render.Error(w, err)
return
}
if len(jws.Signatures) == 0 {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "request body does not contain a signature"))
return
}
if len(jws.Signatures) > 1 {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "request body contains more than one signature"))
return
}
sig := jws.Signatures[0]
uh := sig.Unprotected
if len(uh.KeyID) > 0 ||
uh.JSONWebKey != nil ||
len(uh.Algorithm) > 0 ||
len(uh.Nonce) > 0 ||
len(uh.ExtraHeaders) > 0 {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "unprotected header must not be used"))
return
}
hdr := sig.Protected
switch hdr.Algorithm {
case jose.RS256, jose.RS384, jose.RS512, jose.PS256, jose.PS384, jose.PS512:
if hdr.JSONWebKey != nil {
switch k := hdr.JSONWebKey.Key.(type) {
case *rsa.PublicKey:
if k.Size() < keyutil.MinRSAKeyBytes {
render.Error(w, acme.NewError(acme.ErrorMalformedType,
"rsa keys must be at least %d bits (%d bytes) in size",
8*keyutil.MinRSAKeyBytes, keyutil.MinRSAKeyBytes))
return
}
default:
render.Error(w, acme.NewError(acme.ErrorMalformedType,
"jws key type and algorithm do not match"))
return
}
}
case jose.ES256, jose.ES384, jose.ES512, jose.EdDSA:
// we good
default:
render.Error(w, acme.NewError(acme.ErrorBadSignatureAlgorithmType, "unsuitable algorithm: %s", hdr.Algorithm))
return
}
// Check the validity/freshness of the Nonce.
if err := db.DeleteNonce(ctx, acme.Nonce(hdr.Nonce)); err != nil {
render.Error(w, err)
return
}
// Check that the JWS url matches the requested url.
jwsURL, ok := hdr.ExtraHeaders["url"].(string)
if !ok {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "jws missing url protected header"))
return
}
reqURL := &url.URL{Scheme: "https", Host: r.Host, Path: r.URL.Path}
if jwsURL != reqURL.String() {
render.Error(w, acme.NewError(acme.ErrorMalformedType,
"url header in JWS (%s) does not match request url (%s)", jwsURL, reqURL))
return
}
if hdr.JSONWebKey != nil && len(hdr.KeyID) > 0 {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "jwk and kid are mutually exclusive"))
return
}
if hdr.JSONWebKey == nil && hdr.KeyID == "" {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "either jwk or kid must be defined in jws protected header"))
return
}
next(w, r)
}
}
// extractJWK is a middleware that extracts the JWK from the JWS and saves it
// in the context. Make sure to parse and validate the JWS before running this
// middleware.
func extractJWK(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
db := acme.MustDatabaseFromContext(ctx)
jws, err := jwsFromContext(ctx)
if err != nil {
render.Error(w, err)
return
}
jwk := jws.Signatures[0].Protected.JSONWebKey
if jwk == nil {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "jwk expected in protected header"))
return
}
if !jwk.Valid() {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "invalid jwk in protected header"))
return
}
// Overwrite KeyID with the JWK thumbprint.
jwk.KeyID, err = acme.KeyToID(jwk)
if err != nil {
render.Error(w, acme.WrapErrorISE(err, "error getting KeyID from JWK"))
return
}
// Store the JWK in the context.
ctx = context.WithValue(ctx, jwkContextKey, jwk)
// Get Account OR continue to generate a new one OR continue Revoke with certificate private key
acc, err := db.GetAccountByKeyID(ctx, jwk.KeyID)
switch {
case errors.Is(err, acme.ErrNotFound):
// For NewAccount and Revoke requests ...
break
case err != nil:
render.Error(w, err)
return
default:
if !acc.IsValid() {
render.Error(w, acme.NewError(acme.ErrorUnauthorizedType, "account is not active"))
return
}
ctx = context.WithValue(ctx, accContextKey, acc)
}
next(w, r.WithContext(ctx))
}
}
// checkPrerequisites checks if all prerequisites for serving ACME
// are met by the CA configuration.
func checkPrerequisites(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
// If the function is not set assume that all prerequisites are met.
checkFunc, ok := acme.PrerequisitesCheckerFromContext(ctx)
if ok {
ok, err := checkFunc(ctx)
if err != nil {
render.Error(w, acme.WrapErrorISE(err, "error checking acme provisioner prerequisites"))
return
}
if !ok {
render.Error(w, acme.NewError(acme.ErrorNotImplementedType, "acme provisioner configuration lacks prerequisites"))
return
}
}
next(w, r)
}
}
// lookupJWK loads the JWK associated with the acme account referenced by the
// kid parameter of the signed payload.
// Make sure to parse and validate the JWS before running this middleware.
func lookupJWK(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
db := acme.MustDatabaseFromContext(ctx)
linker := acme.MustLinkerFromContext(ctx)
jws, err := jwsFromContext(ctx)
if err != nil {
render.Error(w, err)
return
}
kidPrefix := linker.GetLink(ctx, acme.AccountLinkType, "")
kid := jws.Signatures[0].Protected.KeyID
if !strings.HasPrefix(kid, kidPrefix) {
render.Error(w, acme.NewError(acme.ErrorMalformedType,
"kid does not have required prefix; expected %s, but got %s",
kidPrefix, kid))
return
}
accID := strings.TrimPrefix(kid, kidPrefix)
acc, err := db.GetAccount(ctx, accID)
switch {
case nosql.IsErrNotFound(err):
render.Error(w, acme.NewError(acme.ErrorAccountDoesNotExistType, "account with ID '%s' not found", accID))
return
case err != nil:
render.Error(w, err)
return
default:
if !acc.IsValid() {
render.Error(w, acme.NewError(acme.ErrorUnauthorizedType, "account is not active"))
return
}
ctx = context.WithValue(ctx, accContextKey, acc)
ctx = context.WithValue(ctx, jwkContextKey, acc.Key)
next(w, r.WithContext(ctx))
return
}
}
}
// extractOrLookupJWK forwards handling to either extractJWK or
// lookupJWK based on the presence of a JWK or a KID, respectively.
func extractOrLookupJWK(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
jws, err := jwsFromContext(ctx)
if err != nil {
render.Error(w, err)
return
}
// at this point the JWS has already been verified (if correctly configured in middleware),
// and it can be used to check if a JWK exists. This flow is used when the ACME client
// signed the payload with a certificate private key.
if canExtractJWKFrom(jws) {
extractJWK(next)(w, r)
return
}
// default to looking up the JWK based on KeyID. This flow is used when the ACME client
// signed the payload with an account private key.
lookupJWK(next)(w, r)
}
}
// canExtractJWKFrom checks if the JWS has a JWK that can be extracted
func canExtractJWKFrom(jws *jose.JSONWebSignature) bool {
if jws == nil {
return false
}
if len(jws.Signatures) == 0 {
return false
}
return jws.Signatures[0].Protected.JSONWebKey != nil
}
// verifyAndExtractJWSPayload extracts the JWK from the JWS and saves it in the context.
// Make sure to parse and validate the JWS before running this middleware.
func verifyAndExtractJWSPayload(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
jws, err := jwsFromContext(ctx)
if err != nil {
render.Error(w, err)
return
}
jwk, err := jwkFromContext(ctx)
if err != nil {
render.Error(w, err)
return
}
if jwk.Algorithm != "" && jwk.Algorithm != jws.Signatures[0].Protected.Algorithm {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "verifier and signature algorithm do not match"))
return
}
payload, err := jws.Verify(jwk)
if err != nil {
render.Error(w, acme.WrapError(acme.ErrorMalformedType, err, "error verifying jws"))
return
}
ctx = context.WithValue(ctx, payloadContextKey, &payloadInfo{
value: payload,
isPostAsGet: len(payload) == 0,
isEmptyJSON: string(payload) == "{}",
})
next(w, r.WithContext(ctx))
}
}
// isPostAsGet asserts that the request is a PostAsGet (empty JWS payload).
func isPostAsGet(next nextHTTP) nextHTTP {
return func(w http.ResponseWriter, r *http.Request) {
payload, err := payloadFromContext(r.Context())
if err != nil {
render.Error(w, err)
return
}
if !payload.isPostAsGet {
render.Error(w, acme.NewError(acme.ErrorMalformedType, "expected POST-as-GET"))
return
}
next(w, r)
}
}
// ContextKey is the key type for storing and searching for ACME request
// essentials in the context of a request.
type ContextKey string
const (
// accContextKey account key
accContextKey = ContextKey("acc")
// jwsContextKey jws key
jwsContextKey = ContextKey("jws")
// jwkContextKey jwk key
jwkContextKey = ContextKey("jwk")
// payloadContextKey payload key
payloadContextKey = ContextKey("payload")
)
// accountFromContext searches the context for an ACME account. Returns the
// account or an error.
func accountFromContext(ctx context.Context) (*acme.Account, error) {
val, ok := ctx.Value(accContextKey).(*acme.Account)
if !ok || val == nil {
return nil, acme.NewError(acme.ErrorAccountDoesNotExistType, "account not in context")
}
return val, nil
}
// jwkFromContext searches the context for a JWK. Returns the JWK or an error.
func jwkFromContext(ctx context.Context) (*jose.JSONWebKey, error) {
val, ok := ctx.Value(jwkContextKey).(*jose.JSONWebKey)
if !ok || val == nil {
return nil, acme.NewErrorISE("jwk expected in request context")
}
return val, nil
}
// jwsFromContext searches the context for a JWS. Returns the JWS or an error.
func jwsFromContext(ctx context.Context) (*jose.JSONWebSignature, error) {
val, ok := ctx.Value(jwsContextKey).(*jose.JSONWebSignature)
if !ok || val == nil {
return nil, acme.NewErrorISE("jws expected in request context")
}
return val, nil
}
// provisionerFromContext searches the context for a provisioner. Returns the
// provisioner or an error.
func provisionerFromContext(ctx context.Context) (acme.Provisioner, error) {
p, ok := acme.ProvisionerFromContext(ctx)
if !ok || p == nil {
return nil, acme.NewErrorISE("provisioner expected in request context")
}
return p, nil
}
// acmeProvisionerFromContext searches the context for an ACME provisioner. Returns
// pointer to an ACME provisioner or an error.
func acmeProvisionerFromContext(ctx context.Context) (*provisioner.ACME, error) {
p, err := provisionerFromContext(ctx)
if err != nil {
return nil, err
}
ap, ok := p.(*provisioner.ACME)
if !ok {
return nil, acme.NewErrorISE("provisioner in context is not an ACME provisioner")
}
return ap, nil
}
// payloadFromContext searches the context for a payload. Returns the payload
// or an error.
func payloadFromContext(ctx context.Context) (*payloadInfo, error) {
val, ok := ctx.Value(payloadContextKey).(*payloadInfo)
if !ok || val == nil {
return nil, acme.NewErrorISE("payload expected in request context")
}
return val, nil
}