Sign merges, CRUD, Wiki and Repository initialisation with gpg key (#7631)

This PR fixes #7598 by providing a configurable way of signing commits across the Gitea instance. Per repository configurability and import/generation of trusted secure keys is not provided by this PR - from a security PoV that's probably impossible to do properly. Similarly web-signing, that is asking the user to sign something, is not implemented - this could be done at a later stage however.

## Features
- [x] If commit.gpgsign is set in .gitconfig sign commits and files created through repofiles. (merges should already have been signed.)
- [x] Verify commits signed with the default gpg as valid
- [x] Signer, Committer and Author can all be different
    - [x] Allow signer to be arbitrarily different - We still require the key to have an activated email on Gitea. A more complete implementation would be to use a keyserver and mark external-or-unactivated with an "unknown" trust level icon.
- [x] Add a signing-key.gpg endpoint to get the default gpg pub key if available
    - Rather than add a fake web-flow user I've added this as an endpoint on /api/v1/signing-key.gpg
    - [x] Try to match the default key with a user on gitea - this is done at verification time
- [x] Make things configurable?
    - app.ini configuration done
    - [x] when checking commits are signed need to check if they're actually verifiable too
- [x] Add documentation

I have decided that adjusting the docker to create a default gpg key is not the correct thing to do and therefore have not implemented this.

3 files changed, 21 insertions, 8 deletions

diff --git a/modules/repofiles/file_test.go b/modules/repofiles/file_test.go
index 7c45139dd9..95ec175ed4 100644
--- a/modules/repofiles/file_test.go
+++ b/modules/repofiles/file_test.go
@@ -73,7 +73,7 @@ func getExpectedFileResponse() *api.FileResponse {
 		},
 		Verification: &api.PayloadCommitVerification{
 			Verified:  false,
-			Reason:    "",
+			Reason:    "gpg.error.not_signed_commit",
 			Signature: "",
 			Payload:   "",
 		},
diff --git a/modules/repofiles/temp_repo.go b/modules/repofiles/temp_repo.go
index 4a50e64192..b07d2a8973 100644
--- a/modules/repofiles/temp_repo.go
+++ b/modules/repofiles/temp_repo.go
@@ -261,7 +261,6 @@ func (t *TemporaryUploadRepository) CommitTree(author, committer *models.User, t
 		return "", fmt.Errorf("Unable to get git version: %v", err)
 	}
 
-	// FIXME: Should we add SSH_ORIGINAL_COMMAND to this
 	// Because this may call hooks we should pass in the environment
 	env := append(os.Environ(),
 		"GIT_AUTHOR_NAME="+authorSig.Name,
@@ -271,13 +270,21 @@ func (t *TemporaryUploadRepository) CommitTree(author, committer *models.User, t
 		"GIT_COMMITTER_EMAIL="+committerSig.Email,
 		"GIT_COMMITTER_DATE="+commitTimeStr,
 	)
+
 	messageBytes := new(bytes.Buffer)
 	_, _ = messageBytes.WriteString(message)
 	_, _ = messageBytes.WriteString("\n")
 
 	args := []string{"commit-tree", treeHash, "-p", "HEAD"}
-	if version.Compare(binVersion, "2.0.0", ">=") {
-		args = append(args, "--no-gpg-sign")
+
+	// Determine if we should sign
+	if version.Compare(binVersion, "1.7.9", ">=") {
+		sign, keyID := t.repo.SignCRUDAction(author, t.basePath, "HEAD")
+		if sign {
+			args = append(args, "-S"+keyID)
+		} else if version.Compare(binVersion, "2.0.0", ">=") {
+			args = append(args, "--no-gpg-sign")
+		}
 	}
 
 	commitHash, stderr, err := process.GetManager().ExecDirEnvStdIn(5*time.Minute,
diff --git a/modules/repofiles/verification.go b/modules/repofiles/verification.go
index 9fc084daaf..3889b7993c 100644
--- a/modules/repofiles/verification.go
+++ b/modules/repofiles/verification.go
@@ -18,10 +18,16 @@ func GetPayloadCommitVerification(commit *git.Commit) *structs.PayloadCommitVeri
 		verification.Signature = commit.Signature.Signature
 		verification.Payload = commit.Signature.Payload
 	}
-	if verification.Reason != "" {
-		verification.Reason = commitVerification.Reason
-	} else if verification.Verified {
-		verification.Reason = "unsigned"
+	if commitVerification.SigningUser != nil {
+		verification.Signer = &structs.PayloadUser{
+			Name:  commitVerification.SigningUser.Name,
+			Email: commitVerification.SigningUser.Email,
+		}
+	}
+	verification.Verified = commitVerification.Verified
+	verification.Reason = commitVerification.Reason
+	if verification.Reason == "" && !verification.Verified {
+		verification.Reason = "gpg.error.not_signed_commit"
 	}
 	return verification
 }