Validation pattern for nickname on login screen

utils.py

@@ -1567,10 +1567,8 @@ def isValidLanguage(text: str) -> bool:
     return False
 
 
-def _isReservedName(nickname: str) -> bool:
-    """Is the given nickname reserved for some special function?
-    """
-    reservedNames = ('inbox', 'dm', 'outbox', 'following',
+def _getReservedWords() -> str:
+    return ('inbox', 'dm', 'outbox', 'following',
             'public', 'followers', 'category',
             'channel', 'calendar',
             'tlreplies', 'tlmedia', 'tlblogs',
@@ -1588,6 +1586,25 @@ def _isReservedName(nickname: str) -> bool:
             'ignores', 'linksmobile', 'newswiremobile',
             'minimal', 'search', 'eventdelete',
             'searchemoji', 'catalog')
+
+
+def getNicknameValidationPattern() -> str:
+    """Returns a html text input validation pattern for nickname
+    """
+    reservedNames = _getReservedWords()
+    pattern = ''
+    for word in reservedNames:
+        if pattern:
+            pattern += '|' + word
+        else:
+            pattern = '[^(' + word
+    return pattern + ')]'
+
+
+def _isReservedName(nickname: str) -> bool:
+    """Is the given nickname reserved for some special function?
+    """
+    reservedNames = _getReservedWords()
     if nickname in reservedNames:
         return True
     return False

webapp_login.py

@@ -12,6 +12,7 @@ import time
 from shutil import copyfile
 from utils import getConfigParam
 from utils import noOfAccounts
+from utils import getNicknameValidationPattern
 from webapp_utils import htmlHeaderWithWebsiteMarkup
 from webapp_utils import htmlFooter
 from webapp_utils import htmlKeyboardNavigation
@@ -152,6 +153,7 @@ def htmlLogin(cssCache: {}, translate: {},
         htmlHeaderWithWebsiteMarkup(cssFilename, instanceTitle,
                                     httpPrefix, domain,
                                     systemLanguage)
+    nicknamePattern = getNicknameValidationPattern()
     instanceTitle = getConfigParam(baseDir, 'instanceTitle')
     loginForm += \
         '<br>\n' + \
@@ -167,8 +169,8 @@ def htmlLogin(cssCache: {}, translate: {},
         '    <label for="nickname"><b>' + \
         translate['Nickname'] + '</b></label>\n' + \
         '    <input type="text" ' + autocompleteStr + ' placeholder="' + \
-        translate['Enter Nickname'] + \
-        '" name="username" required autofocus>\n' + \
+        translate['Enter Nickname'] + '" name="username" ' + \
+        'pattern="' + nicknamePattern + '" required autofocus>\n' + \
         '\n' + \
         '    <label for="password"><b>' + \
         translate['Password'] + '</b></label>\n' + \