Allow registering with email if no ID Server

If the server advertises that it supports doing so

This version uses a random me.dbkr prefix until the MSC is
written.

Requires https://github.com/matrix-org/matrix-js-sdk/pull/1017
Implements https://github.com/matrix-org/matrix-doc/pull/2233

src/components/structures/auth/Registration.js

@@ -98,6 +98,9 @@ module.exports = React.createClass({
             // component without it.
             matrixClient: null,
 
+            // the capabilities object from the server
+            serverCaps: null,
+
             // The user ID we've just registered
             registeredUsername: null,
 
@@ -204,13 +207,24 @@ module.exports = React.createClass({
         }
 
         const {hsUrl, isUrl} = serverConfig;
-        this.setState({
-            matrixClient: Matrix.createClient({
-                baseUrl: hsUrl,
-                idBaseUrl: isUrl,
-            }),
+        const cli = Matrix.createClient({
+            baseUrl: hsUrl,
+            idBaseUrl: isUrl,
+        });
+
+        let caps = null;
+        try {
+            caps = await cli.getServerCapabilities();
+            caps = caps || {};
+        } catch (e) {
+            console.log("Unable to fetch server capabilities", e);
+        }
+
+        this.setState({
+            matrixClient: cli,
+            serverCaps: caps,
+            busy: false,
         });
-        this.setState({busy: false});
         try {
             await this._makeRegisterRequest({});
             // This should never succeed since we specified an empty
@@ -523,7 +537,7 @@ module.exports = React.createClass({
             />;
         } else if (!this.state.matrixClient && !this.state.busy) {
             return null;
-        } else if (this.state.busy || !this.state.flows) {
+        } else if (this.state.busy || !this.state.flows | this.state.serverCaps === null) {
             return <div className="mx_AuthBody_spinner">
                 <Spinner />
             </div>;
@@ -550,6 +564,7 @@ module.exports = React.createClass({
                 flows={this.state.flows}
                 serverConfig={this.props.serverConfig}
                 canSubmit={!this.state.serverErrorIsFatal}
+                serverCapabilities={this.state.serverCaps}
             />;
         }
     },

src/components/views/auth/RegistrationForm.js

@@ -55,6 +55,7 @@ module.exports = React.createClass({
         flows: PropTypes.arrayOf(PropTypes.object).isRequired,
         serverConfig: PropTypes.instanceOf(ValidatedServerConfig).isRequired,
         canSubmit: PropTypes.bool,
+        serverCapabilities: PropTypes.object,
     },
 
     getDefaultProps: function() {
@@ -436,8 +437,9 @@ module.exports = React.createClass({
     },
 
     _showEmail() {
+        const idServerRequired = !this.props.serverCapabilities['me.dbkr.idomyownemail'];
         const haveIs = Boolean(this.props.serverConfig.isUrl);
-        if (!haveIs || !this._authStepIsUsed('m.login.email.identity')) {
+        if ((idServerRequired && !haveIs) || !this._authStepIsUsed('m.login.email.identity')) {
             return false;
         }
         return true;