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, 105 insertions, 6 deletions

diff --git a/templates/repo/commit_page.tmpl b/templates/repo/commit_page.tmpl
index 0cfdf5156d..5b19523cf2 100644
--- a/templates/repo/commit_page.tmpl
+++ b/templates/repo/commit_page.tmpl
@@ -26,6 +26,16 @@
 						<img class="ui avatar image" src="{{AvatarLink .Commit.Author.Email}}" />
 						<strong>{{.Commit.Author.Name}}</strong>
 					{{end}}
+					{{if or (ne .Commit.Committer.Name .Commit.Author.Name) (ne .Commit.Committer.Email .Commit.Author.Email)}}
+						<span> </span>
+						{{if ne .Verification.CommittingUser.ID 0}}
+							<img class="ui avatar image" src="{{.Verification.CommittingUser.RelAvatarLink}}" />
+							<a href="{{.Verification.CommittingUser.HomeLink}}"><strong>{{.Commit.Committer.Name}}</strong></a> <{{.Commit.Committer.Email}}>
+						{{else}}
+							<img class="ui avatar image" src="{{AvatarLink .Commit.Committer.Email}}" />
+							<strong>{{.Commit.Committer.Name}}</strong>
+						{{end}}
+					{{end}}
 					<span class="text grey" id="authored-time">{{TimeSince .Commit.Author.When $.Lang}}</span>
 				</div>
 				<div class="seven wide right aligned column">
@@ -50,15 +60,36 @@
 		{{if .Commit.Signature}}
 			{{if .Verification.Verified }}
 				<div class="ui bottom attached positive message">
-				  <i class="green lock icon"></i>
-					<span>{{.i18n.Tr "repo.commits.signed_by"}}:</span>
-					<a href="{{.Verification.SigningUser.HomeLink}}"><strong>{{.Commit.Committer.Name}}</strong></a> <{{.Commit.Committer.Email}}>
-					<span class="pull-right"><span>{{.i18n.Tr "repo.commits.gpg_key_id"}}:</span> {{.Verification.SigningKey.KeyID}}</span>
+					{{if ne .Verification.SigningUser.ID 0}}
+						<i class="green lock icon"></i>
+						<span>{{.i18n.Tr "repo.commits.signed_by"}}:</span>
+						<img class="ui avatar image" src="{{.Verification.SigningUser.RelAvatarLink}}" />
+						<a href="{{.Verification.SigningUser.HomeLink}}"><strong>{{.Verification.SigningUser.Name}}</strong></a> <{{.Verification.SigningEmail}}>
+						<span class="pull-right"><span>{{.i18n.Tr "repo.commits.gpg_key_id"}}:</span> {{.Verification.SigningKey.KeyID}}</span>
+					{{else}}
+						<i class="icons" title="{{.i18n.Tr "gpg.default_key"}}">
+							<i class="green lock icon"></i>
+							<i class="tiny inverted cog icon centerlock"></i>
+						</i>
+						<span>{{.i18n.Tr "repo.commits.signed_by"}}:</span>
+						<img class="ui avatar image" src="{{AvatarLink .Verification.SigningEmail}}" />
+						<strong>{{.Verification.SigningUser.Name}}</strong> <{{.Verification.SigningEmail}}>
+						<span class="pull-right"><span>{{.i18n.Tr "repo.commits.gpg_key_id"}}:</span> <i class="cogs icon" title="{{.i18n.Tr "gpg.default_key"}}"></i>{{.Verification.SigningKey.KeyID}}</span>
+					{{end}}
+				</div>
+			{{else if .Verification.Warning}}
+				<div class="ui bottom attached message">
+				  <i class="red unlock icon"></i>
+				  <span class="red text">{{.i18n.Tr .Verification.Reason}}</span>
+				  <span class="pull-right"><span class="red text">{{.i18n.Tr "repo.commits.gpg_key_id"}}:</span> <i class="red warning icon"></i>{{.Verification.SigningKey.KeyID}}</span>
 				</div>
 			{{else}}
 				<div class="ui bottom attached message">
 				  <i class="grey unlock icon"></i>
 				  {{.i18n.Tr .Verification.Reason}}
+				  {{if and .Verification.SigningKey (ne .Verification.SigningKey.KeyID "")}}
+					<span class="pull-right"><span class="red text">{{.i18n.Tr "repo.commits.gpg_key_id"}}:</span> <i class="red warning icon"></i>{{.Verification.SigningKey.KeyID}}</span>
+				  {{end}}
 				</div>
 			{{end}}
 		{{end}}
diff --git a/templates/repo/commits_table.tmpl b/templates/repo/commits_table.tmpl
index e11bbee0e8..09a2c072b1 100644
--- a/templates/repo/commits_table.tmpl
+++ b/templates/repo/commits_table.tmpl
@@ -56,12 +56,21 @@
 							{{end}}
 						</td>
 						<td class="sha">
-							<a rel="nofollow" class="ui sha label {{if .Signature}} isSigned {{if .Verification.Verified }} isVerified {{end}}{{end}}" href="{{AppSubUrl}}/{{$.Username}}/{{$.Reponame}}/commit/{{.ID}}">
+							<a rel="nofollow" class="ui sha label {{if .Signature}} isSigned {{if .Verification.Verified }} isVerified {{else if .Verification.Warning}} isWarning {{end}}{{end}}" href="{{AppSubUrl}}/{{$.Username}}/{{$.Reponame}}/commit/{{.ID}}">
 								{{ShortSha .ID.String}}
 								{{if .Signature}}
 									<div class="ui detail icon button">
 										{{if .Verification.Verified}}
-											<i title="{{.Verification.Reason}}" class="lock green icon"></i>
+											{{if ne .Verification.SigningUser.ID 0}}
+												<i title="{{.Verification.Reason}}" class="lock green icon"></i>
+											{{else}}
+												<i title="{{.Verification.Reason}}" class="icons">
+													<i class="green lock icon"></i>
+													<i class="tiny inverted cog icon centerlock"></i>
+												</i>
+											{{end}}
+										{{else if .Verification.Warning}}
+											<i title="{{$.i18n.Tr .Verification.Reason}}" class="red unlock icon"></i>
 										{{else}}
 											<i title="{{$.i18n.Tr .Verification.Reason}}" class="unlock icon"></i>
 										{{end}}
diff --git a/templates/swagger/v1_json.tmpl b/templates/swagger/v1_json.tmpl
index d8750d8bcc..5be36d23be 100644
--- a/templates/swagger/v1_json.tmpl
+++ b/templates/swagger/v1_json.tmpl
@@ -5140,6 +5140,42 @@
         }
       }
     },
+    "/repos/{owner}/{repo}/signing-key.gpg": {
+      "get": {
+        "produces": [
+          "text/plain"
+        ],
+        "tags": [
+          "repository"
+        ],
+        "summary": "Get signing-key.gpg for given repository",
+        "operationId": "repoSigningKey",
+        "parameters": [
+          {
+            "type": "string",
+            "description": "owner of the repo",
+            "name": "owner",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "string",
+            "description": "name of the repo",
+            "name": "repo",
+            "in": "path",
+            "required": true
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "GPG armored public key",
+            "schema": {
+              "type": "string"
+            }
+          }
+        }
+      }
+    },
     "/repos/{owner}/{repo}/stargazers": {
       "get": {
         "produces": [
@@ -5691,6 +5727,26 @@
         }
       }
     },
+    "/signing-key.gpg": {
+      "get": {
+        "produces": [
+          "text/plain"
+        ],
+        "tags": [
+          "miscellaneous"
+        ],
+        "summary": "Get default signing-key.gpg",
+        "operationId": "getSigningKey",
+        "responses": {
+          "200": {
+            "description": "GPG armored public key",
+            "schema": {
+              "type": "string"
+            }
+          }
+        }
+      }
+    },
     "/teams/{id}": {
       "get": {
         "produces": [
@@ -9525,6 +9581,9 @@
           "type": "string",
           "x-go-name": "Signature"
         },
+        "signer": {
+          "$ref": "#/definitions/PayloadUser"
+        },
         "verified": {
           "type": "boolean",
           "x-go-name": "Verified"