Initial commit

CalDAV and CardDAV checkers sharing a single Go module. Discovery follows
RFC 6764 (/.well-known + SRV/TXT), authenticated probes cover principal,
home-set, collections and a minimal REPORT query on top of go-webdav.
Common shape in internal/dav/; CalDAV adds a scheduling rule.

Surfaces its context URL (and each secure-SRV target) as TLS endpoints via
the EndpointDiscoverer interface, so the dedicated TLS checker can pick
them up without re-parsing observations.

HTML report foregrounds common misconfigs (well-known returning 200,
missing SRV, plaintext-only SRV, missing DAV capability, skipped auth
phase) as action-item callouts before the full phase breakdown.

internal/dav/options_shared.go

@@ -0,0 +1,61 @@
+package dav
+
+// CommonOptions returns the CheckerOptionField descriptors shared by both
+// CalDAV and CardDAV checkers. Each checker composes them into its own
+// CheckerOptionsDocumentation alongside protocol-specific tweaks.
+//
+// Returning plain CheckerOptionField slices (from the SDK) keeps this package
+// free of any sdk import cycles: the caller already depends on the SDK.
+import (
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// UserOptions are editable in the checker settings UI.
+func UserOptions() []sdk.CheckerOptionDocumentation {
+	return []sdk.CheckerOptionDocumentation{
+		{
+			Id:          "username",
+			Type:        "string",
+			Label:       "Username",
+			Description: "Optional. Supplying credentials unlocks authenticated checks (principal, home-set, collections, report probe).",
+		},
+		{
+			Id:          "password",
+			Type:        "string",
+			Label:       "Password or token",
+			Description: "Optional. Paired with the username for HTTP Basic authentication.",
+			Secret:      true,
+		},
+		{
+			Id:          "context_url",
+			Type:        "string",
+			Label:       "Explicit context URL",
+			Description: "Optional. Bypasses /.well-known and SRV discovery — use for servers with a non-standard layout.",
+			Placeholder: "https://dav.example.com/caldav/",
+		},
+	}
+}
+
+// DomainOptions are auto-filled per-domain by happyDomain.
+func DomainOptions() []sdk.CheckerOptionDocumentation {
+	return []sdk.CheckerOptionDocumentation{
+		{
+			Id:       "domain_name",
+			Label:    "Domain name",
+			AutoFill: sdk.AutoFillDomainName,
+		},
+	}
+}
+
+// RunOptions are set at collect-time only.
+func RunOptions() []sdk.CheckerOptionDocumentation {
+	return []sdk.CheckerOptionDocumentation{
+		{
+			Id:          "timeout_seconds",
+			Type:        "number",
+			Label:       "Timeout (seconds)",
+			Description: "Per-request HTTP timeout.",
+			Default:     float64(10),
+		},
+	}
+}