Certificates Renewal + SSE

- Certificate renewal is just a re-request as it's forced already
- Rejig the routes for readability
- Added Server Side Events so that the UI would invalidate the
cache when changes happen on the backend, such as certs being
provided or failing
- Added a SSE Token, which has the same shelf life as normal token
but can't be used interchangeably. The reason for this is, the
SSE endpoint needs a token for auth as a Query param, so it would
be stored in log files. If someone where to get a hold of that,
it's pretty useless as it can't be used to change anything, only
to listen for events until it expires
- Added test endpoint for SSE testing only availabe in debug mode

backend/internal/serverevents/sse.go

@@ -0,0 +1,74 @@
+package serverevents
+
+import (
+	"encoding/json"
+	"net/http"
+	"npm/internal/logger"
+
+	"github.com/jc21/go-sse"
+)
+
+var instance *sse.Server
+
+const defaultChannel = "changes"
+
+// Message is how we're going to send the data
+type Message struct {
+	Lang       string            `json:"lang,omitempty"`
+	LangParams map[string]string `json:"lang_params,omitempty"`
+	Type       string            `json:"type,omitempty"`
+	Affects    string            `json:"affects,omitempty"`
+}
+
+// Get will return a sse server
+func Get() *sse.Server {
+	if instance == nil {
+		instance = sse.NewServer(&sse.Options{
+			Logger: logger.Get(),
+			ChannelNameFunc: func(request *http.Request) string {
+				return defaultChannel // This is the channel for all updates regardless of visibility
+			},
+		})
+	}
+	return instance
+}
+
+// Shutdown will shutdown the server
+func Shutdown() {
+	if instance != nil {
+		instance.Shutdown()
+	}
+}
+
+// SendChange will send a specific change
+func SendChange(affects string) {
+	Send(Message{Affects: affects}, "")
+}
+
+// SendMessage will construct a message for the UI
+func SendMessage(typ, lang string, langParams map[string]string) {
+	Send(Message{
+		Type:       typ,
+		Lang:       lang,
+		LangParams: langParams,
+	}, "")
+}
+
+// Send will send a message
+func Send(msg Message, channel string) {
+	if channel == "" {
+		channel = defaultChannel
+	}
+	logger.Debug("SSE Sending: %+v", msg)
+	if data, err := json.Marshal(msg); err != nil {
+		logger.Error("SSEError", err)
+	} else {
+		Get().SendMessage(channel, sse.SimpleMessage(string(data)))
+	}
+}
+
+// TODO: if we end up implementing user visibility,
+// then we'll have to subscribe people to their own
+// channels and publish to all or some depending on visibility.
+// This means using a specific ChannelNameFunc that revolves
+// around the user and their visibility.