add user registration routes

* Added /register get and post routes.
+ Added default attributes to AnonymousUser, including a new
  AnonymousList which behaves like an sqlalchemy relationship
  list.
+ aurweb.util: Added validation functions for various user fields
  used throughout registration.
+ test_accounts_routes: Added get|post register route tests.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/util.py

@@ -1,7 +1,91 @@
+import base64
 import random
+import re
 import string
 
+from urllib.parse import urlparse
+
+import jinja2
+
+from email_validator import EmailNotValidError, EmailUndeliverableError, validate_email
+
+import aurweb.config
+
 
 def make_random_string(length):
     return ''.join(random.choices(string.ascii_lowercase +
                                   string.digits, k=length))
+
+
+def valid_username(username):
+    min_len = aurweb.config.getint("options", "username_min_len")
+    max_len = aurweb.config.getint("options", "username_max_len")
+    if not (min_len <= len(username) <= max_len):
+        return False
+
+    # Check that username contains: one or more alphanumeric
+    # characters, an optional separator of '.', '-' or '_', followed
+    # by alphanumeric characters.
+    return re.match(r'^[a-zA-Z0-9]+[.\-_]?[a-zA-Z0-9]+$', username)
+
+
+def valid_email(email):
+    try:
+        validate_email(email)
+    except EmailUndeliverableError:
+        return False
+    except EmailNotValidError:
+        return False
+    return True
+
+
+def valid_homepage(homepage):
+    parts = urlparse(homepage)
+    return parts.scheme in ("http", "https") and bool(parts.netloc)
+
+
+def valid_password(password):
+    min_len = aurweb.config.getint("options", "passwd_min_len")
+    return len(password) >= min_len
+
+
+def valid_pgp_fingerprint(fp):
+    fp = fp.replace(" ", "")
+    try:
+        # Attempt to convert the fingerprint to an int via base16.
+        # If it can't, it's not a hex string.
+        int(fp, 16)
+    except ValueError:
+        return False
+
+    # Check the length; must be 40 hexadecimal digits.
+    return len(fp) == 40
+
+
+def valid_ssh_pubkey(pk):
+    valid_prefixes = ("ssh-rsa", "ecdsa-sha2-nistp256",
+                      "ecdsa-sha2-nistp384", "ecdsa-sha2-nistp521",
+                      "ssh-ed25519")
+
+    has_valid_prefix = False
+    for prefix in valid_prefixes:
+        if "%s " % prefix in pk:
+            has_valid_prefix = True
+            break
+    if not has_valid_prefix:
+        return False
+
+    tokens = pk.strip().rstrip().split(" ")
+    if len(tokens) < 2:
+        return False
+
+    return base64.b64encode(base64.b64decode(tokens[1])).decode() == tokens[1]
+
+
+@jinja2.contextfilter
+def account_url(context, user):
+    request = context.get("request")
+    base = f"{request.url.scheme}://{request.url.hostname}"
+    if request.url.scheme == "http" and request.url.port != 80:
+        base += f":{request.url.port}"
+    return f"{base}/account/{user.Username}"