[#525] ir/container: Verify operations with session token

Session token can be presented `Put`, `Delete` and `SetEACL` notification
events. IR should consider this case as issuing a power of attorney to a
third party. Thus, checking the eligibility for an operation should be
complicated:

 - token owner should be the owner of the related container;
 - the intent must be signed with a session key;
 - the power of attorney must be signed by the owner of the container.

Omitted checks (TBD):

 - session token should have container session context;
 - the verb of the context should correspond to the operation.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/innerring/processors/container/common.go

@@ -1,18 +1,51 @@
 package container
 
 import (
+	"bytes"
 	"crypto/ecdsa"
+	"crypto/elliptic"
+	"errors"
 	"fmt"
 
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/nspcc-dev/neofs-api-go/pkg/owner"
+	"github.com/nspcc-dev/neofs-api-go/pkg/session"
+	"github.com/nspcc-dev/neofs-api-go/util/signature"
+	signature2 "github.com/nspcc-dev/neofs-api-go/v2/signature"
 )
 
 type ownerIDSource interface {
 	OwnerID() *owner.ID
 }
 
+func tokenFromEvent(src interface {
+	SessionToken() []byte
+}) (*session.Token, error) {
+	binToken := src.SessionToken()
+
+	if len(binToken) == 0 {
+		return nil, nil
+	}
+
+	tok := session.NewToken()
+
+	err := tok.Unmarshal(binToken)
+	if err != nil {
+		return nil, fmt.Errorf("could not unmarshal session token: %w", err)
+	}
+
+	return tok, nil
+}
+
 func (cp *Processor) checkKeyOwnership(ownerIDSrc ownerIDSource, key *keys.PublicKey) error {
+	if tokenSrc, ok := ownerIDSrc.(interface {
+		SessionToken() *session.Token
+	}); ok {
+		if token := tokenSrc.SessionToken(); token != nil {
+			return cp.checkKeyOwnershipWithToken(ownerIDSrc, key, tokenSrc.SessionToken())
+		}
+	}
+
 	// TODO: need more convenient way to do this
 	w, err := owner.NEO3WalletFromPublicKey(&ecdsa.PublicKey{
 		X: key.X,
@@ -40,3 +73,55 @@ func (cp *Processor) checkKeyOwnership(ownerIDSrc ownerIDSource, key *keys.Publi
 
 	return fmt.Errorf("key %s is not tied to the owner of the container", key)
 }
+
+func (cp *Processor) checkKeyOwnershipWithToken(ownerIDSrc ownerIDSource, key *keys.PublicKey, token *session.Token) error {
+	// check session key
+	if !bytes.Equal(
+		key.Bytes(),
+		token.SessionKey(),
+	) {
+		return errors.New("signed with a non-session key")
+	}
+
+	// check owner
+	// TODO: need Equal method on owner.ID
+	if token.OwnerID().String() != ownerIDSrc.OwnerID().String() {
+		return errors.New("owner differs with token owner")
+	}
+
+	err := cp.checkSessionToken(token)
+	if err != nil {
+		return fmt.Errorf("invalid session token: %w", err)
+	}
+
+	return nil
+}
+
+func (cp *Processor) checkSessionToken(token *session.Token) error {
+	// verify signature
+
+	// TODO: need more convenient way to do this
+	//  e.g. provide VerifySignature method from Token
+
+	// FIXME: do all so as not to deepen in the version
+	tokenV2 := token.ToV2()
+
+	signWrapper := signature2.StableMarshalerWrapper{
+		SM: tokenV2.GetBody(),
+	}
+	if err := signature.VerifyDataWithSource(signWrapper, func() (key, sig []byte) {
+		tokenSignature := tokenV2.GetSignature()
+		return tokenSignature.GetKey(), tokenSignature.GetSign()
+	}); err != nil {
+		return errors.New("invalid signature")
+	}
+
+	// check token owner's key ownership
+
+	key, err := keys.NewPublicKeyFromBytes(token.Signature().Key(), elliptic.P256())
+	if err != nil {
+		return fmt.Errorf("invalid key: %w", err)
+	}
+
+	return cp.checkKeyOwnership(token, key)
+}