Follows and relationships (#27)

* Follows -- create and undo, both remote and local
* Statuses -- federate new posts, including media, attachments, CWs and image descriptions.

internal/api/security/useragentblock.go

@@ -0,0 +1,43 @@
+/*
+   GoToSocial
+   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package security
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+// UserAgentBlock is a middleware that prevents google chrome cohort tracking by
+// writing the Permissions-Policy header after all other parts of the request have been completed.
+// See: https://plausible.io/blog/google-floc
+func (m *Module) UserAgentBlock(c *gin.Context) {
+
+	ua := c.Request.UserAgent()
+	if ua == "" {
+		c.AbortWithStatus(http.StatusTeapot)
+		return
+	}
+
+	if strings.Contains(strings.ToLower(c.Request.UserAgent()), strings.ToLower("friendica")) {
+		c.AbortWithStatus(http.StatusTeapot)
+		return
+	}
+}