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.

1 files changed, 54 insertions, 6 deletions

diff --git a/models/repo.go b/models/repo.go
index d8a462c37b..06708d24ab 100644
--- a/models/repo.go
+++ b/models/repo.go
@@ -38,6 +38,7 @@ import (
 	"code.gitea.io/gitea/modules/timeutil"
 
 	"github.com/go-xorm/xorm"
+	"github.com/mcuadros/go-version"
 	"github.com/unknwon/com"
 	ini "gopkg.in/ini.v1"
 	"xorm.io/builder"
@@ -1126,7 +1127,20 @@ func CleanUpMigrateInfo(repo *Repository) (*Repository, error) {
 }
 
 // initRepoCommit temporarily changes with work directory.
-func initRepoCommit(tmpPath string, sig *git.Signature) (err error) {
+func initRepoCommit(tmpPath string, u *User) (err error) {
+	commitTimeStr := time.Now().Format(time.RFC3339)
+
+	sig := u.NewGitSig()
+	// Because this may call hooks we should pass in the environment
+	env := append(os.Environ(),
+		"GIT_AUTHOR_NAME="+sig.Name,
+		"GIT_AUTHOR_EMAIL="+sig.Email,
+		"GIT_AUTHOR_DATE="+commitTimeStr,
+		"GIT_COMMITTER_NAME="+sig.Name,
+		"GIT_COMMITTER_EMAIL="+sig.Email,
+		"GIT_COMMITTER_DATE="+commitTimeStr,
+	)
+
 	var stderr string
 	if _, stderr, err = process.GetManager().ExecDir(-1,
 		tmpPath, fmt.Sprintf("initRepoCommit (git add): %s", tmpPath),
@@ -1134,10 +1148,29 @@ func initRepoCommit(tmpPath string, sig *git.Signature) (err error) {
 		return fmt.Errorf("git add: %s", stderr)
 	}
 
-	if _, stderr, err = process.GetManager().ExecDir(-1,
+	binVersion, err := git.BinVersion()
+	if err != nil {
+		return fmt.Errorf("Unable to get git version: %v", err)
+	}
+
+	args := []string{
+		"commit", fmt.Sprintf("--author='%s <%s>'", sig.Name, sig.Email),
+		"-m", "Initial commit",
+	}
+
+	if version.Compare(binVersion, "1.7.9", ">=") {
+		sign, keyID := SignInitialCommit(tmpPath, u)
+		if sign {
+			args = append(args, "-S"+keyID)
+		} else if version.Compare(binVersion, "2.0.0", ">=") {
+			args = append(args, "--no-gpg-sign")
+		}
+	}
+
+	if _, stderr, err = process.GetManager().ExecDirEnv(-1,
 		tmpPath, fmt.Sprintf("initRepoCommit (git commit): %s", tmpPath),
-		git.GitExecutable, "commit", fmt.Sprintf("--author='%s <%s>'", sig.Name, sig.Email),
-		"-m", "Initial commit"); err != nil {
+		env,
+		git.GitExecutable, args...); err != nil {
 		return fmt.Errorf("git commit: %s", stderr)
 	}
 
@@ -1189,9 +1222,24 @@ func getRepoInitFile(tp, name string) ([]byte, error) {
 }
 
 func prepareRepoCommit(e Engine, repo *Repository, tmpDir, repoPath string, opts CreateRepoOptions) error {
+	commitTimeStr := time.Now().Format(time.RFC3339)
+	authorSig := repo.Owner.NewGitSig()
+
+	// Because this may call hooks we should pass in the environment
+	env := append(os.Environ(),
+		"GIT_AUTHOR_NAME="+authorSig.Name,
+		"GIT_AUTHOR_EMAIL="+authorSig.Email,
+		"GIT_AUTHOR_DATE="+commitTimeStr,
+		"GIT_COMMITTER_NAME="+authorSig.Name,
+		"GIT_COMMITTER_EMAIL="+authorSig.Email,
+		"GIT_COMMITTER_DATE="+commitTimeStr,
+	)
+
 	// Clone to temporary path and do the init commit.
-	_, stderr, err := process.GetManager().Exec(
+	_, stderr, err := process.GetManager().ExecDirEnv(
+		-1, "",
 		fmt.Sprintf("initRepository(git clone): %s", repoPath),
+		env,
 		git.GitExecutable, "clone", repoPath, tmpDir,
 	)
 	if err != nil {
@@ -1282,7 +1330,7 @@ func initRepository(e Engine, repoPath string, u *User, repo *Repository, opts C
 		}
 
 		// Apply changes and commit.
-		if err = initRepoCommit(tmpDir, u.NewGitSig()); err != nil {
+		if err = initRepoCommit(tmpDir, u); err != nil {
 			return fmt.Errorf("initRepoCommit: %v", err)
 		}
 	}