resolving issue with login redirects through setting SSL scheme

.env.template

 FLASK_DEBUG=
 SECRET_KEY=
 DATABASE_URL=sqlite:///db.sqlite
+SSL_SCHEME=
 
 # MariaDB variables (for production only)
 MYSQL_ROOT_PASSWORD=

web/app/auth.py

 from flask_login import login_user, logout_user, login_required
 from .models import User
 from . import db
+import os
 
 auth = Blueprint('auth', __name__)
 
     # take the user-supplied password, hash it, and compare it to the hashed password in the database
     if not user or not check_password_hash(user.password, password):
         flash('Please check your login details and try again.')
-        return redirect(url_for('auth.login',_external=True)) # if the user doesn't exist or password is wrong, reload the page
+        return redirect(url_for('auth.login',_external=True,_scheme=os.environ.get('SSL_SCHEME'))) # if the user doesn't exist or password is wrong, reload the page
 
     # if the above check passes, then we know the user has the right credentials
     login_user(user, remember=remember)
-    flash(url_for('main.profile',_external=True))
-    return redirect(url_for('main.profile',_external=True))
+    flash(url_for('main.profile',_external=True,_scheme=os.environ.get('SSL_SCHEME')))
+    return redirect(url_for('main.profile',_external=True,_scheme=os.environ.get('SSL_SCHEME')))
 
 # routes for signup page
 @auth.route('/signup')
 
     if user: # if a user is found, we want to redirect back to signup page so user can try again
         flash('Email address already exists')
-        return redirect(url_for('auth.signup',_external=True))
+        return redirect(url_for('auth.signup',_external=True,_scheme=os.environ.get('SSL_SCHEME')))
 
     # create a new user with the form data. Hash the password so the plaintext version isn't saved.
     new_user = User(email=email, name=name, password=generate_password_hash(password, method='sha256'))
     db.session.add(new_user)
     db.session.commit()
 
-    return redirect(url_for('auth.login',_external=True))
+    return redirect(url_for('auth.login',_external=True,_scheme=os.environ.get('SSL_SCHEME')))
 
 # route for logout function
 @auth.route('/logout')
 @login_required
 def logout():
     logout_user()
-    return redirect(url_for('main.index',_external=True))
+    return redirect(url_for('main.index',_external=True,_scheme=os.environ.get('SSL_SCHEME')))