Rename serverkeyapi to signingkeyserver (#1492)

* Rename serverkeyapi to signingkeyserver

We use "api" for public facing stuff and "server" for internal stuff.
As the server key API is internal only, we call it 'signing key server',
which also clarifies the type of key (as opposed to TLS keys, E2E keys, etc)

* Convert docker/scripts to use signing-key-server

* Rename missed bits

internal/config/config_signingkeyserver.go

@@ -0,0 +1,52 @@
+package config
+
+import "github.com/matrix-org/gomatrixserverlib"
+
+type SigningKeyServer struct {
+	Matrix *Global `yaml:"-"`
+
+	InternalAPI InternalAPIOptions `yaml:"internal_api"`
+
+	// The SigningKeyServer database caches the public keys of remote servers.
+	// It may be accessed by the FederationAPI, the ClientAPI, and the MediaAPI.
+	Database DatabaseOptions `yaml:"database"`
+
+	// Perspective keyservers, to use as a backup when direct key fetch
+	// requests don't succeed
+	KeyPerspectives KeyPerspectives `yaml:"key_perspectives"`
+
+	// Should we prefer direct key fetches over perspective ones?
+	PreferDirectFetch bool `yaml:"prefer_direct_fetch"`
+}
+
+func (c *SigningKeyServer) Defaults() {
+	c.InternalAPI.Listen = "http://localhost:7780"
+	c.InternalAPI.Connect = "http://localhost:7780"
+	c.Database.Defaults()
+	c.Database.ConnectionString = "file:signingkeyserver.db"
+}
+
+func (c *SigningKeyServer) Verify(configErrs *ConfigErrors, isMonolith bool) {
+	checkURL(configErrs, "signing_key_server.internal_api.listen", string(c.InternalAPI.Listen))
+	checkURL(configErrs, "signing_key_server.internal_api.bind", string(c.InternalAPI.Connect))
+	checkNotEmpty(configErrs, "signing_key_server.database.connection_string", string(c.Database.ConnectionString))
+}
+
+// KeyPerspectives are used to configure perspective key servers for
+// retrieving server keys.
+type KeyPerspectives []KeyPerspective
+
+type KeyPerspective struct {
+	// The server name of the perspective key server
+	ServerName gomatrixserverlib.ServerName `yaml:"server_name"`
+	// Server keys for the perspective user, used to verify the
+	// keys have been signed by the perspective server
+	Keys []KeyPerspectiveTrustKey `yaml:"keys"`
+}
+
+type KeyPerspectiveTrustKey struct {
+	// The key ID, e.g. ed25519:auto
+	KeyID gomatrixserverlib.KeyID `yaml:"key_id"`
+	// The public key in base64 unpadded format
+	PublicKey string `yaml:"public_key"`
+}