add login redirect query param to login button

atst/routes/__init__.py

@@ -1,3 +1,4 @@
+import urllib.parse as url
 from flask import Blueprint, render_template, g, redirect, session, url_for, request
 
 from flask import current_app as app
@@ -16,7 +17,15 @@ bp = Blueprint("atst", __name__)
 
 @bp.route("/")
 def root():
-    return render_template("login.html")
+    redirect_url = app.config.get("CAC_URL")
+    if request.args.get("next"):
+        redirect_url = url.urljoin(
+            redirect_url, "?{}".format(url.urlencode(request.args))
+        )
+
+    return render_template(
+        "login.html", redirect=bool(request.args.get("next")), redirect_url=redirect_url
+    )
 
 
 @bp.route("/help")

templates/login.html

@@ -15,13 +15,20 @@
 
           <img class="login-banner__logo" src="/static/img/ccpo-logo.svg" alt="Cloud Computing Program Office Logo">
 
-          <a class="usa-button usa-button-big login-banner__button" href='{{ config.get('CAC_URL','https://cac.atat.codes') }}'><span>Sign in with CAC</span></a>
+          <a class="usa-button usa-button-big login-banner__button" href='{{ redirect_url }}'><span>Sign in with CAC</span></a>
 
           {% if g.dev %}
-            <a class="usa-button usa-button-big usa-button-secondary" href='/login-dev'><span>DEV Login</span></a>
+          <a class="usa-button usa-button-big usa-button-secondary" href='{{ url_for("dev.login_dev", **request.args) }}'><span>DEV Login</span></a>
           {% endif %}
         </div>
 
+        {% if redirect %}
+          {{ Alert('Log in Required.',
+              message='After you log in, you will be redirected to your destination page.',
+              level='warning'
+          ) }}
+        {% endif %}
+
         {{ Alert('Certificate Selection',
           message='When you are prompted to select a certificate, please select <strong>E-mail Certificate</strong> from the provided choices.',
           actions=[