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, 59 insertions, 0 deletions

diff --git a/modules/git/repo_gpg.go b/modules/git/repo_gpg.go
new file mode 100644
index 0000000000..b4c3f3b431
--- /dev/null
+++ b/modules/git/repo_gpg.go
@@ -0,0 +1,59 @@
+// Copyright 2015 The Gogs Authors. All rights reserved.
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package git
+
+import (
+	"fmt"
+	"strings"
+
+	"code.gitea.io/gitea/modules/process"
+)
+
+// LoadPublicKeyContent will load the key from gpg
+func (gpgSettings *GPGSettings) LoadPublicKeyContent() error {
+	content, stderr, err := process.GetManager().Exec(
+		"gpg -a --export",
+		"gpg", "-a", "--export", gpgSettings.KeyID)
+	if err != nil {
+		return fmt.Errorf("Unable to get default signing key: %s, %s, %v", gpgSettings.KeyID, stderr, err)
+	}
+	gpgSettings.PublicKeyContent = content
+	return nil
+}
+
+// GetDefaultPublicGPGKey will return and cache the default public GPG settings for this repository
+func (repo *Repository) GetDefaultPublicGPGKey(forceUpdate bool) (*GPGSettings, error) {
+	if repo.gpgSettings != nil && !forceUpdate {
+		return repo.gpgSettings, nil
+	}
+
+	gpgSettings := &GPGSettings{
+		Sign: true,
+	}
+
+	value, _ := NewCommand("config", "--get", "commit.gpgsign").RunInDir(repo.Path)
+	sign, valid := ParseBool(strings.TrimSpace(value))
+	if !sign || !valid {
+		gpgSettings.Sign = false
+		repo.gpgSettings = gpgSettings
+		return gpgSettings, nil
+	}
+
+	signingKey, _ := NewCommand("config", "--get", "user.signingkey").RunInDir(repo.Path)
+	gpgSettings.KeyID = strings.TrimSpace(signingKey)
+
+	defaultEmail, _ := NewCommand("config", "--get", "user.email").RunInDir(repo.Path)
+	gpgSettings.Email = strings.TrimSpace(defaultEmail)
+
+	defaultName, _ := NewCommand("config", "--get", "user.name").RunInDir(repo.Path)
+	gpgSettings.Name = strings.TrimSpace(defaultName)
+
+	if err := gpgSettings.LoadPublicKeyContent(); err != nil {
+		return nil, err
+	}
+	repo.gpgSettings = gpgSettings
+	return repo.gpgSettings, nil
+}