[feature] Add global instance CSS customization setting (#3352)

Allow instance admins to add custom CSS that will affect
every page of their instance.

This is done with a new CustomCSS instance setting that
works pretty much exactly like the Users CustomCSS property.
This custom CSS is then requested for every page load.
User styles/themes take precedence over this CSS.

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/internal/web/customcss.go b/internal/web/customcss.go
index b4072f2a7..36ae9de55 100644
--- a/internal/web/customcss.go
+++ b/internal/web/customcss.go
@@ -55,3 +55,22 @@ func (m *Module) customCSSGETHandler(c *gin.Context) {
 	c.Header(cacheControlHeader, cacheControlNoCache)
 	c.Data(http.StatusOK, textCSSUTF8, []byte(customCSS))
 }
+
+func (m *Module) instanceCustomCSSGETHandler(c *gin.Context) {
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.TextCSS); err != nil {
+		apiutil.WebErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	instanceV1, errWithCode := m.processor.InstanceGetV1(c.Request.Context())
+	if errWithCode != nil {
+		apiutil.WebErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	instanceCustomCSS := instanceV1.CustomCSS
+
+	c.Header(cacheControlHeader, cacheControlNoCache)
+	c.Data(http.StatusOK, textCSSUTF8, []byte(instanceCustomCSS))
+}