Hardcode ott-username input name in DefaultLoginPageGeneratingFilter

- GenerateOneTimeTokenFilter uses `"username"`, the default UI should use the same parameter name

Author: Kehrlann

web/src/main/java/org/springframework/security/web/authentication/ui/DefaultLoginPageGeneratingFilter.java

@@ -242,8 +242,8 @@ private String generateLoginPageHtml(HttpServletRequest request, boolean loginEr
 			sb.append("        <h2>Request a One-Time Token</h2>\n");
 			sb.append(createError(loginError, errorMsg) + createLogoutSuccess(logoutSuccess) + "<p>\n");
 			sb.append("          <label for=\"ott-username\" class=\"screenreader\">Username</label>\n");
-			sb.append("          <input type=\"text\" id=\"ott-username\" name=\"" + this.usernameParameter
-					+ "\" placeholder=\"Username\" required>\n");
+			sb.append(
+					"          <input type=\"text\" id=\"ott-username\" name=\"username\" placeholder=\"Username\" required>\n");
 			sb.append("        </p>\n");
 			sb.append(renderHiddenInputs(request));
 			sb.append("          <button class=\"primary\" type=\"submit\" form=\"ott-form\">Send Token</button>\n");

web/src/test/java/org/springframework/security/web/authentication/DefaultLoginPageGeneratingFilterTests.java

@@ -199,7 +199,7 @@ public void generateWhenOneTimeTokenLoginThenOttForm() throws Exception {
 				        <h2>Request a One-Time Token</h2>
 				<p>
 				          <label for="ott-username" class="screenreader">Username</label>
-				          <input type="text" id="ott-username" name="null" placeholder="Username" required>
+				          <input type="text" id="ott-username" name="username" placeholder="Username" required>
 				        </p>
 				          <button class="primary" type="submit" form="ott-form">Send Token</button>
 				      </form>