4.2. Hosting the task pane

The task pane is a collection of static files (HTML, JS, CSS, icons, manifest.xml) produced by the webpack build and shipped in the site/ subfolder of toa-client-<version>.zip. It can be served from any HTTPS origin the customer controls - nginx, IIS, Apache, Azure Static Web Apps, or an internal CDN.

4.2.1. Required properties of the origin

HTTPS with a publicly trusted certificate. Outlook refuses to load resources from origins with invalid certificates, and the add-in will simply not render.
Same origin for the static bundle and the API. The add-in calls the TOA server using the relative base path /api/...; a reverse proxy on the same origin must forward those requests to the Spring Boot backend. This keeps the browser happy with one cookie scope, avoids CORS entirely, and sidesteps mixed-content rules.
HTTP compression (gzip or brotli) on *.js, *.html, *.css is recommended - the bundle is a few hundred kB uncompressed.

4.2.2. Example nginx configuration

server {
    listen 443 ssl http2;
    server_name addin.customer.cz;

    ssl_certificate     /etc/ssl/addin/fullchain.pem;
    ssl_certificate_key /etc/ssl/addin/privkey.pem;

    root  /var/www/toa-addin/site;
    index taskpane.html;

    # Static bundle: everything under /, with cache-busting on JS
    # chunks (webpack hashes filenames).
    location / {
        try_files $uri =404;
    }

    # Reverse proxy to the TOA server. Keep the /api/ prefix in the
    # public URL but strip it before forwarding so the server sees
    # the native paths declared in tao-openapi.yml.
    location /api/ {
        proxy_pass         http://127.0.0.1:8080/;
        proxy_set_header   Host               $host;
        proxy_set_header   X-Forwarded-For    $proxy_add_x_forwarded_for;
        proxy_set_header   X-Forwarded-Proto  $scheme;
    }
}

4.2.3. TLS and certificates

If the customer uses Let’s Encrypt or a corporate PKI, certificate renewal is out of scope for TOA itself. Just make sure the reverse-proxy and the TOA server are not exposed via different hostnames - the add-in assumes a single origin.

4.2.4. Cache and versioning

Webpack writes hashed filenames for JS and asset chunks (taskpane.<hash>.js), so aggressive browser caching on those is safe. The two files that change without a filename hash are taskpane.html and manifest.xml; serve those with Cache-Control: no-cache or a short max-age so that updates propagate within minutes of a redeploy.

Outlook itself caches the manifest for several hours after the user logs in; see Centralized deployment (Microsoft 365) for how to force a refresh through the admin center.