[WIP] proposal for new oidc and fulcio abstractions

internal/pkg/cosign/fulcio/attestor.go

@@ -0,0 +1,101 @@
+// Copyright 2022 The Sigstore Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fulcio
+
+import (
+	"bytes"
+	"context"
+	"crypto"
+	"encoding/base64"
+	"encoding/json"
+	"io"
+
+	"github.com/secure-systems-lab/go-securesystemslib/dsse"
+	"github.com/sigstore/cosign/internal/pkg/cosign"
+	"github.com/sigstore/cosign/internal/pkg/cosign/oidc"
+	"github.com/sigstore/cosign/pkg/oci"
+	"github.com/sigstore/cosign/pkg/oci/static"
+	"github.com/sigstore/cosign/pkg/types"
+	"github.com/sigstore/sigstore/pkg/signature"
+)
+
+type attestor struct {
+	signer      signature.Signer
+	oidp        oidc.Provider
+	payloadType string
+}
+
+var _ cosign.DSSEAttestor = (*attestor)(nil)
+
+// Attest implements `cosign.DSSEAttestor`
+func (pa *attestor) DSSEAttest(ctx context.Context, payload io.Reader) (oci.Signature, crypto.PublicKey, error) {
+	p, err := io.ReadAll(payload)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	pb := dsse.PAE(pa.payloadType, p)
+
+	sig, err := pa.signer.SignMessage(bytes.NewReader(pb))
+	if err != nil {
+		return nil, nil, err
+	}
+	pk, err := pa.signer.PublicKey()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	envelope := dsse.Envelope{
+		PayloadType: pa.payloadType,
+		Payload:     base64.StdEncoding.EncodeToString(pb),
+		Signatures: []dsse.Signature{{
+			Sig: base64.StdEncoding.EncodeToString(sig),
+		}},
+	}
+
+	envelopeJSON, err := json.Marshal(envelope)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	opts := []static.Option{static.WithLayerMediaType(types.DssePayloadType)}
+
+	att, err := static.NewAttestation(envelopeJSON, opts...)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return att, pk, nil
+}
+
+// NewDSSEAttestor returns a `cosign.DSSEAttestor`
+func NewDSSEAttestor(payloadType string,
+	s signature.Signer, oidp oidc.Provider) cosign.DSSEAttestor {
+	return &attestor{
+		signer:      s,
+		payloadType: payloadType,
+		oidp:        oidp,
+	}
+}
+
+func NewKeylessDSSEAttestor(payloadType string, oidp oidc.Provider) cosign.DSSEAttestor {
+	var s signature.Signer
+	// create an ephemeral keypair...
+	return &attestor{
+		signer:      s,
+		payloadType: payloadType,
+		oidp:        oidp,
+	}
+}

internal/pkg/cosign/fulcio/client.go

@@ -0,0 +1,62 @@
+// Copyright 2022 The Sigstore Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package fulcio
+
+import (
+	"context"
+	"crypto/ecdsa"
+	"crypto/x509"
+	"errors"
+	"strings"
+
+	"github.com/sigstore/cosign/internal/pkg/cosign/oidc"
+	fulcioapi "github.com/sigstore/fulcio/pkg/api"
+	"github.com/sigstore/sigstore/pkg/signature"
+)
+
+// *NOTE* This is a higher-level client than exists in `sigstore/fulcio`, should probably live there
+
+// Client is a Fulcio client.
+type Client struct {
+	APIClient fulcioapi.Client
+}
+
+// GetCert retrieves a Fulcio certificate which associates the `Signer`'s public key with the ID provided
+func (c *Client) GetCert(ctx context.Context, signer signature.Signer, oidp oidc.Provider) (cert *x509.Certificate, chain []*x509.Certificate, sct []byte, err error) {
+	idToken, err := oidp.GetIDToken(ctx)
+	// Sign the token's subject
+	subject := ""
+	// subject := idToken.Subject
+	subjectSig, err := signer.SignMessage(strings.NewReader(subject))
+
+	pub, err := signer.PublicKey()
+	if _, isECDSA := pub.(*ecdsa.PublicKey); !isECDSA {
+		return nil, nil, nil, errors.New("only ESCDA public keys are supported...?")
+	}
+	pubBytes, err := x509.MarshalPKIXPublicKey(pub)
+
+	req := fulcioapi.CertificateRequest{
+		PublicKey: fulcioapi.Key{
+			Algorithm: "ecdsa",
+			Content:   pubBytes,
+		},
+		SignedEmailAddress: subjectSig,
+	}
+
+	resp, err := c.APIClient.SigningCert(req, idToken.JWTEncode())
+	// cert = parsex509(resp.CertPEM)
+	// chain = parsex509(resp.ChainPEM)
+	return cert, chain, resp.SCT, nil
+}

internal/pkg/cosign/oidc/oidc.go

@@ -0,0 +1,54 @@
+// Copyright 2022 The Sigstore Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package oidc
+
+import (
+	"context"
+
+	"golang.org/x/oauth2"
+)
+
+// *NOTE* Most if not all of this should live in `sigstore/sigstore`
+
+// IDToken is an OpenID ID token.
+type IDToken struct { // OR use https://pkg.go.dev/github.com/coreos/go-oidc#IDToken (or something) instead?
+	// our own impl of https://openid.net/specs/openid-connect-core-1_0.html#IDToken
+}
+
+func (t *IDToken) JWTEncode() string {
+	return "TODO"
+}
+
+func JWTDecodeIDToken(rawIDToken string) (*IDToken, error) {
+	return &IDToken{}, nil
+}
+
+// Provider describes an OpenID Provider.
+type Provider interface {
+	// GetIDToken returns an *IDToken
+	GetIDToken(context.Context) (*IDToken, error)
+}
+
+// PotempkinProvider is a make-believe `Provider` implementation to throw rocks at.
+// There should be one for each OAuth flow type (https://connect2id.com/learn/openid-connect#auth-request) we want to support.
+type PotempkinProvider struct {
+	oauthConfig oauth2.Config // token endpoints, client_id, client_secret, etc.
+}
+
+// GetIDToken implements Provider
+func (p *PotempkinProvider) GetIDToken(context.Context) (*IDToken, error) {
+	// TODO
+	return &IDToken{}, nil
+}