svchost/auth: static credentials source

This uses an in-memory table of credentials keyed on hostname. This is
the simplest possible credentials source that can actually return
credentials, and is suitable for representing statically-configured
credentials from configuration.

svchost/auth/static.go

@@ -0,0 +1,28 @@
+package auth
+
+import (
+	"github.com/hashicorp/terraform/svchost"
+)
+
+// StaticCredentialsSource is a credentials source that retrieves credentials
+// from the provided map. It returns nil if a requested hostname is not
+// present in the map.
+//
+// The caller should not modify the given map after passing it to this function.
+func StaticCredentialsSource(creds map[svchost.Hostname]map[string]interface{}) CredentialsSource {
+	return staticCredentialsSource(creds)
+}
+
+type staticCredentialsSource map[svchost.Hostname]map[string]interface{}
+
+func (s staticCredentialsSource) ForHost(host svchost.Hostname) (HostCredentials, error) {
+	if s == nil {
+		return nil, nil
+	}
+
+	if m, exists := s[host]; exists {
+		return HostCredentialsFromMap(m), nil
+	}
+
+	return nil, nil
+}

svchost/auth/static_test.go

@@ -0,0 +1,38 @@
+package auth
+
+import (
+	"testing"
+
+	"github.com/hashicorp/terraform/svchost"
+)
+
+func TestStaticCredentialsSource(t *testing.T) {
+	src := StaticCredentialsSource(map[svchost.Hostname]map[string]interface{}{
+		svchost.Hostname("example.com"): map[string]interface{}{
+			"token": "abc123",
+		},
+	})
+
+	t.Run("exists", func(t *testing.T) {
+		creds, err := src.ForHost(svchost.Hostname("example.com"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if tokCreds, isToken := creds.(HostCredentialsToken); isToken {
+			if got, want := string(tokCreds), "abc123"; got != want {
+				t.Errorf("wrong token %q; want %q", got, want)
+			}
+		} else {
+			t.Errorf("creds is %#v; want HostCredentialsToken", creds)
+		}
+	})
+	t.Run("does not exist", func(t *testing.T) {
+		creds, err := src.ForHost(svchost.Hostname("example.net"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if creds != nil {
+			t.Errorf("creds is %#v; want nil", creds)
+		}
+	})
+}