Extract login utils out of two_factor view

This better reflects how the code is reused in other views and is
not specific to two factor actions. We have a pattern of testing
utility functionality for each view (as opposed to testing the util
+ the view calls the util), so I'm leaving the tests as-is.

app/main/views/two_factor.py

@@ -17,7 +17,11 @@ from app.main import main
 from app.main.forms import TwoFactorForm
 from app.models.user import User
 from app.utils import is_less_than_days_ago
-from app.utils.login import redirect_to_sign_in
+from app.utils.login import (
+    log_in_user,
+    redirect_to_sign_in,
+    redirect_when_logged_in,
+)
 
 
 @main.route('/two-factor-email-sent', methods=['GET'])
@@ -97,38 +101,3 @@ def revalidate_email_sent():
     title = 'Email resent' if request.args.get('email_resent') else 'Check your email'
     redirect_url = request.args.get('next')
     return render_template('views/re-validate-email-sent.html', title=title, redirect_url=redirect_url)
-
-
-# see http://flask.pocoo.org/snippets/62/
-def _is_safe_redirect_url(target):
-    from urllib.parse import urljoin, urlparse
-    host_url = urlparse(request.host_url)
-    redirect_url = urlparse(urljoin(request.host_url, target))
-    return redirect_url.scheme in ('http', 'https') and \
-        host_url.netloc == redirect_url.netloc
-
-
-def log_in_user(user_id):
-    try:
-        user = User.from_id(user_id)
-        # the user will have a new current_session_id set by the API - store it in the cookie for future requests
-        session['current_session_id'] = user.current_session_id
-        # Check if coming from new password page
-        if 'password' in session.get('user_details', {}):
-            user.update_password(session['user_details']['password'], validated_email_access=True)
-        user.activate()
-        user.login()
-    finally:
-        # get rid of anything in the session that we don't expect to have been set during register/sign in flow
-        session.pop("user_details", None)
-        session.pop("file_uploads", None)
-
-    return redirect_when_logged_in(platform_admin=user.platform_admin)
-
-
-def redirect_when_logged_in(platform_admin):
-    next_url = request.args.get('next')
-    if next_url and _is_safe_redirect_url(next_url):
-        return redirect(next_url)
-
-    return redirect(url_for('main.show_accounts_or_dashboard'))