Explicit Proxy — How It Works

How Explicit Proxy Processes Traffic

After you’ve set up explicit proxy, here’s how it works. Follow along to see the path traffic takes:
  1. The mobile user browses the Internet or accesses the SaaS application by entering the URL or IP address using a web browser.
  2. The browser on the mobile users’ endpoint checks for the PAC file.
    This PAC file specifies that the URL or SaaS request should be forwarded to Prisma Access explicit proxy.
  3. The HTTPS client (the browser on the mobile user’s endpoint) forwards the URL request to the proxy URL.
  4. The traffic is redirected to the explicit proxy, and the proxy decrypts the traffic.
  5. The proxy inspects the traffic and checks for the authentication cookie set up by the Prisma Access explicit proxy.
    The cookie contains information that identifies the mobile user, and uses the cookie to authenticate the user.
  6. If, upon inspection of the cookie, Prisma Access determines that the user has not been authenticated, it redirects the user for authentication.
  7. After the IdP authenticates the user, Prisma Access stores the authentication state of the user in the Authentication Cache Service (ACS). The validity period of the authentication is based on the
    Cookie Lifetime
    value you specify during explicit proxy configuration.
  8. The explicit proxy checks for the presence and validity of our cookie. If the cookie is not present or is invalid, the user is redirected to ACS. After ACS confirms the authentication of the user, the user is redirected back to the explicit proxy with a token. The proxy then validates that token and sets the cookie for that domain for that user.
  9. Prisma Access applies security enforcement based on the security policy rules that the administrator has configured.
  10. If the URL is not blocked by security policy rules, Prisma Access sends the URL request to the internet.

How Explicit Proxy Identifies Users

Explicit Proxy identifies users in the traffic logs dependent on how the users authenticate with the proxy, as shown in the following table.
Authentication Type
User Identification in Traffic Logs
Users that are logged in using SAML authentication and decryption
The username.
Users that are logged in from another proxy that uses X-Authenticated-User (XAU) headers
XAU header information.
Explicit Proxy only allows traffic from specific IP addresses to use XAU for authentication. You create an address object and specify the IP addresses where you allow XAU for authentication; then, add the address object in the
Trusted Source Address
field during Explicit Proxy setup.
Authenticated cross-origin resource sharing (CORS) requests
To help identify traffic that is coming from authenticated users in cases where browsers cannot send cookies or perform authentication redirection, such as CORS requests, Explicit Proxy adds the
to the traffic logs.
Undecrypted traffic (if you have allowed Explicit Proxy to allow undecrypted traffic from IP addresses where users have previously authenticated)
You can specify Explicit Proxy to allow undecrypted traffic from IP addresses where users have authenticated; to do so, specify
Decrypt traffic that matches existing decryption rules; for undecrypted traffic, allow traffic only from known IPs registered by authenticated users
during Explicit Proxy setup. In these configurations, Explicit Proxy adds the
to the traffic logs.

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