This document explains the processes for Web Authentication on a Wireless LAN Controller (WLC).
Cisco recommends that you have basic knowledge of WLC configuration.
The information in this document is based on all WLC hardware models.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
Web authentication (WebAuth) is Layer 3 security. It allows for user-friendly security that works on any station that runs a browser. It can also be combined with any pre-shared key (PSK) security (Layer 2 security policy). Although the combination of WebAuth and PSK reduces the user-friendly portion significantly and is not used often, it still has the advantage to encrypt client traffic. WebAuth is an authentication method without encryption.
WebAuth cannot be configured with 802.1x/RADIUS (Remote Authentication Dial-In User Service) until the WLC Software Release 7.4 is installed where it can be configured at the same time. However, be aware that clients must go through both dot1x and web authentication. It is not meant for guest, but for the addition of a web portal for employees (who use 802.1x). There is not an all-in-one service set identifier (SSID) for dot1x for employees or web portal for guests.
How WebAuth Works
The 802.11 authentication process is open, so you can authenticate and associate without any problems. After that, you are associated, but not in the WLC RUN state. With web authentication enabled, you are kept in WEBAUTH_REQD where you cannot access any network resource (no ping, and so on). You must receive a DHCP IP address with the address of the DNS server in the options.
You must type a valid URL in your browser. The client resolves the URL through the DNS protocol. The client then sends its HTTP request to the IP address of the website. The WLC intercepts that request and returns the webauth login page, which spoofs the website IP address. In the case of an external WebAuth, the WLC replies with an HTTP response that includes your website IP address and states that the page has moved. The page was moved to the external web server used by the WLC. When you are authenticated, you gain access to all of the network resources and are redirected to the URL originally requested, by default (unless a forced redirect was configured on the WLC). In summary, the WLC allows the client to resolve the DNS and get an IP address automatically in WEBAUTH_REQD state.
Tip: If you want the WLC to watch another port instead of port 80, you can use config network web-auth-port <port number> to create a redirect on this port also. An example is the Access Control Server (ACS) web interface, which is on port 2002 or other similar applications.
Note about HTTPS Redirection: By default and in the 7.x versions and earlier, the WLC did not redirect HTTPS traffic. This means that if you open your browser and type an HTTPS address, nothing happens. You must type an HTTP address in order to get redirected to the login page which was served in HTTPS.
In Version 8.0 and later, you can enable redirection of HTTPS traffic with the CLI command config network web-auth https-redirect enable.
Be aware that this is resource consuming for the WLC in case many HTTPS requests are sent. Also note that a certificate warning is unavoidable in this case. Indeed, if your client requests any URL (such as https://www.cisco.com), the WLC still presents its own certificate issued for the virtual interface IP address. This will obviously never match the URL/IP address requested by client and the certificate will not be trusted unless the client forces the exception in his browser.
Indicative performance drop measured :
3 URLs - HTTP
140 / second
1st URL - HTTP
2nd and 3rd URLs - HTTPS
20 / second
3 URLs - HTTPS (large deployment)
< 1 / second
3 URLs - HTTPS (max of 100 clients)
10 / second
In this performance table, the 3 URLs are referred to as:
The original URL entered by the end-user (the website the user wants to browse to)
The URL the WLC redirects the browser to
The final credentials submission
The performance table gives the WLC performance in case all 3 URLs are HTTP, in case all 3 URLs are HTTPS, or if the client moves from HTTP to HTTPS (the more typical scenario).
How to Make an Internal (Local) WebAuth Work with an Internal Page
If you need to configure a WLAN with an operational dynamic interface, the clients should also receive a DNS server IP address through DHCP. Before you set any webauth, you should test that your WLAN works properly, that you can resolve DNS requests (nslookup), and that you can browse web pages. Then, you can set the web authentication as Layer 3 security features. You can create your users in the local database or on an external RADIUS server, for example. Refer to the Wireless LAN Controller Web Authentication Configuration Example document.
How to Configure a Custom Local WebAuth with Custom Page
Custom webauth can be configured with redirectUrl from the Security tab. This forces a redirect to a specific web page you enter. When the user is authenticated, it overrides the original URL the client requested and displays the page for which the redirect was assigned.
The custom feature allows you to use a custom HTML page instead of the default login page. Upload your html and image files bundle to the controller. In the upload page, look for webauth bundle in a tar format. Usually, PicoZip creates tars that work compatibly with the WLC. For an example of a WebAuth bundle, refer to the Download Software page for Wireless Controller WebAuth Bundles. Be sure to select the appropriate release for your WLC. A good recommendation is to customize a bundle that exists; do not create a bundle from scratch.
There are some limitations with custom webauth that vary with versions and bugs. Things to watch for include:
the .tar file size (no more than 5MB)
the number of files in the .tar
the filename length of the files (should be no more than 30 characters)
For each WLAN, you configure with the override global config command and set a WebAuth type for each WLAN. This means you can have an internal/default WebAuth with a custom internal/default WebAuth for another WLAN. This also allows you to configure different custom pages for each WLAN. You must combine all your pages in the same bundle and upload them to the WLC. Then, you can set your custom page with the override global config command on each WLAN and select which file is the login page from all of the files within the bundle. You can choose a different login page inside the bundle for each WLAN.
There is a variable within the HTML bundle that allows the redirection. Do not put your forced redirection URL there. For any redirection issues in custom WebAuth, Cisco recommends to check the bundle. If you enter a redirect URL with += in the WLC GUI, this could overwrite or add to the URL defined inside the bundle. For example, in the WLC GUI, the redirectURL field is set to www.cisco.com; however, in the bundle it shows: redirectURL+= 'www.google.com'. The += redirects users to www.cisco.comwww.google.com, which is an invalid URL.
How to Make an External (Local) Web Authentication Work with an External Page
As already briefly explained, the utilization of an external WebAuth server is just an external repository for the login page. The user credentials are still authenticated by the WLC. The external web server only allows you to use a special or different login page. Here are the steps performed for an external WebAuth:
The client (end user) opens a web browser and enters a URL.
If the client is not authenticated and external web authentication is used, the WLC redirects the user to the external web server URL. In other words, the WLC sends an HTTP redirect to the client with the website's spoofed IP address and points to the external server IP address. The external web authentication login URL is appended with parameters such as the AP_Mac_Address, the client_url (www.website.com), and the action_URL that the customer needs to contact the switch web server.
The external web server URL sends the user to a login page. Then the user can use a pre-authentication access control list (ACL) in order to access the server. The ACL is needed for all WLC models except 4400 series and Wism1.
The login page takes the user credentials input and sends the request back to the action_URL, such as http://22.214.171.124/login.html, of the WLC web server. This is provided as an input parameter to the customer redirect URL, where 126.96.36.199 is the virtual interface address on the switch.
The WLC web server submits the username and password for authentication.
The WLC initiates the RADIUS server request or uses the local database on the WLC, and then authenticates the user.
If authentication is successful, the WLC web server either forwards the user to the configured redirect URL or to the URL the client entered.
If authentication fails, then the WLC web server redirects the user back to the customer login URL.
This is a variation of the internal web authentication. It displays a page with a warning or an alert statement, but does not prompt for credentials. The user should click ok. You can enable email input, and the user can enter their email address, which becomes their username. When the user is connected, check your active clients list; that user is listed with the email address they entered as the username. For more information, refer to the Wireless LAN Controller Web Passthrough Configuration Example.
Conditional Web Redirect
If you enable a conditional web redirect, the user is conditionally redirected to a particular web page after 802.1x authentication has successfully completed. You can specify the redirect page and the conditions under which the redirect occurs on your RADIUS server. Conditions can include the user's password when it reaches the expiration date or when the user needs to pay a bill for continued use/access. If the RADIUS server returns the Cisco AV-pair url-redirect, then the user is redirected to the specified URL when they open a browser. If the server also returns the Cisco AV-pair url-redirect-acl, then the specified ACL is installed as a pre-authentication ACL for this client. The client is not considered fully authorized at this point and can only pass traffic allowed by the pre-authentication ACL. After the client completes a particular operation at the specified URL (for example, a password change or bill payment), then the client must re-authenticate. When the RADIUS server does not return a url-redirect, the client is considered fully authorized and allowed to pass traffic.
Note: The conditional web redirect feature is available only for WLANs that are configured for 802.1x or WPA+WPA2 Layer 2 security.
If you enable splash page web redirect, the user is redirected to a particular web page after 802.1x authentication has completed successfully. After the redirect, the user has full access to the network. You can specify the redirect page on your RADIUS server. If the RADIUS server returns the Cisco AV-pair url-redirect, then the user is redirected to the specified URL when they open a browser. The client is considered fully authorized at this point and is allowed to pass traffic, even if the RADIUS server does not return a url-redirect.
Note: The splash page web redirect feature is available only for WLANs that are configured for 802.1x or WPA+WPA2 Layer 2 security.
After you configure the RADIUS server, you can then configure the splash page web redirect on the controller with the controller GUI or CLI.
WebAuth on MAC Filter Failure
This requires you to configure MAC filters on the Layer 2 security menu. If users are successfully validated with their MAC addresses, then they go directly to the run state. If they are not, then they go to the WEBAUTH_REQD state and the normal web authentication occurs.
Central Web Authentication
Central Web Authentication refers to a scenario where the WLC no longer hosts any services. The difference resides in the fact that the client is directly sent to the ISE web portal and does not go through 188.8.131.52 on the WLC. The login page and the entire portal are externalized.
Central Web Authentication takes place when you have RADIUS Network Admission Control (NAC) enabled in the advanced settings of the WLAN and MAC filters enabled.
The overall concept is that the WLC sends a RADIUS authentication (usually for the MAC filter) to ISE, which replies with the redirect-url attribute value (AV) pair. The user is then put in POSTURE_REQD state until ISE gives the authorization with a Change of Authorization (CoA) request. The same scenario happens in Posture or Central WebAuth. Central WebAuth is not compatible with WPA-Enterprise/802.1x because the guest portal cannot return session keys for encryption like it does with Extensible Authentication Protocol (EAP).
External User Authentication (RADIUS)
This is only valid for Local WebAuth when WLC handles the credentials, or when a Layer 3 web policy is enabled. You can then either authenticate users locally on the WLC or externally via RADIUS.
There is an order in which the WLC checks for the credentials of the user.
In any case, it first looks in its own database.
If it does not find the users there, it goes to the RADIUS server configured in the guest WLAN (if there is one configured).
It then checks in the global RADIUS server list against the RADIUS servers where network user is checked.
This third point is very important and answers the question of many who do not configure RADIUS for that WLAN, but notice that it still checks against the RADIUS when the user is not found on the controller. This is because network user is checked against your RADIUS servers in the global list.
WLC can authenticate users to RADIUS server with Password Authentication Protocol (PAP), Challenge Handshake Authentication Protocol (CHAP) or EAP-MD5 (Message Digest5). This is a global parameter and is configurable from GUI or CLI:
From GUI: navigate to Controller > Web RADIUS Authentication
From CLI: enter config custom-web RADIUSauth <pap|chap|md5chap>
Note: The NAC guest server only uses PAP.
How to set a Wired Guest WLAN
It is easy to configure and very close to the wireless guest configuration. You can configure it with one or two controllers (only if one is auto-anchor).
Choose a VLAN as the VLAN in which you place wired guest users, for example, on VLAN 50. When a wired guest wants access to the Internet, plug the laptop to a port on a switch configured for VLAN 50. This VLAN 50 must be allowed and present on the path through the WLC trunk port. In a case of two WLCs (one anchor and one foreign), this wired guest VLAN must lead to the foreign WLC (named WLC1) and not to the anchor. WLC1 then takes care of tunneling the traffic to the DMZ WLC (the anchor, named WLC2), which releases the traffic in the routed network.
Here are the five steps to configure wired guest access:
Configure a dynamic interface (VLAN) for wired guest user access.
On WLC1, create a dynamic interface VLAN50. In the interface configuration page, check the Guest LAN box. Then, fields such as IP address and gateway disappear. The only thing your WLC needs to know about this interface is that traffic is routed from VLAN 50. These clients are wired guests.
Create a wired LAN for guest user access.
On a controller, an interface is used when associated to a WLAN. The second step is to create a WLAN on your main office controllers. Navigate to WLANs and click New. In WLAN Type, choose Guest LAN.
In Profile Name and WLAN SSID, enter a name that identifies this WLAN. These names can be different, but cannot contain spaces. The term WLAN is used, but this network profile is not related to wireless network profile.
The General tab offers two drop-down lists: Ingress and Egress. Ingress is the VLAN from which users come (VLAN 50); Egress is the VLAN to which you want to send them.
For Ingress, choose VLAN50.
For Egress, it is different. If you have only one controller, you need to create another dynamic interface, a standard one this time (not a guest LAN), and you send your wired users to this interface. In this case, send them to the DMZ controller. Therefore, for the Egress interface, choose the Management Interface.
The Security mode for this Guest LAN "WLAN" is WebAuth, which is acceptable. Click Ok in order to validate.
Configure the foreign controller (main office).
From the WLAN list, click Mobility Anchor at the end of the Guest LAN line, and choose your DMZ controller. It is assumed here that both controllers know each other. If they do not know each other yet, go to Controller > Mobility Management > Mobility group, and add DMZWLC on WLC1. Then add WLC1 on DMZ. Both controllers should not be in the same mobility group. Otherwise, basic security rules are broken.
Configure the anchor controller (the DMZ controller).
Your main office controller is ready. You now need to prepare your DMZ controller. Open a web browser session to your DMZ controller and navigate to WLANs. Create a new WLAN. In WLAN Type, choose Guest LAN.
In Profile Name and WLAN SSID, enter a name that identifies this WLAN. Use the same values as entered on the main office controller.
The Ingress interface here is None. It actually does not matter, because the traffic is received through the Ethernet over IP (EoIP) tunnel. This is why you do not need to specify any Ingress interface.
The Egress interface is the one on which the clients are supposed to be sent. For example, the DMZ VLAN is VLAN 9. Create a standard dynamic interface for VLAN 9 on your DMZWLC, then choose VLAN 9 as the Egress interface.
You need to configure the end of the Mobility Anchor tunnel. From the WLAN list, choose Mobility Anchor for Guest LAN. Send the traffic to the local controller, DMZWLC. Both ends are now ready.
Fine-tune the guest LAN.
You can also fine-tune the WLAN settings on both ends. Be careful, the settings must be identical on both ends. For example, if you choose to click in the WLAN Advanced tab, Allow AAA override on WLC1, you need to check the same box on DMZWLC. If there are any differences in the selections in the WLAN on either side, the tunnel breaks. DMZWLC refuses the traffic; you can see when you run debug mobility.
Keep in mind that all values are actually obtained from DMZWLC: IP addresses, VLAN values, and so on. Configure the WLC1 side identically, so that it relays the request to the WLCDMZ.
Certificates for the Login Page
This section provides the processes you need to follow if you want to put your own certificate on the WebAuth page, or if you want to hide the 184.108.40.206 WebAuth URL and display a named URL.
Upload a Certificate for the Controller Web Authentication
Through the GUI (WebAuth > Certificate) or CLI (transfer type webauthcert) you can upload a certificate on the controller. Whether it is a certificate you created with your certificate authority (CA) or a third-party official certificate, it must be in .pem format. Before you send, you must also enter the key of the certificate.
After the upload, a reboot is required in order for the certificate to be in place. Once rebooted, go to the WebAuth certificate page in the GUI and it shows you the details of the certificate you uploaded (validity and so on). The important field is the common name (CN), which is the name issued to the certificate. This field is discussed in this document under the section "Certificate Authority and Other Certificates on the Controller".
After you have rebooted and verified the details of the certificate, you are presented with the new controller certificate on the WebAuth login page. However, there can be two situations.
If your certificate has been issued by one of the few main root CAs that every computer trusts, then it is okay. An example is VeriSign, but you are usually signed by a Verisign sub-CA and not the root CA. You can check in your browser certificate store if you see the CA mentioned there as trusted.
If you got your certificate from a smaller company/CA, all computers do not trust them. You should provide the company/CA certificate to the client as well, and hopefully one of the root CAs will issue that certificate. Eventually, you end up with a chain such as "Certificate has been issued by CA x > CA x certificate has been issued by CA y > CA y certificate has been issued by this trusted root CA". The end goal is to reach a CA that the client does trust.
Certificate Authority and Other Certificates on the Controller
In order to be rid of the warning "this certificate is not trusted", you must also enter the certificate of the CA that issued the controller certificate on the controller. Then the controller presents both certificates (controller's certificate and its CA certificate). The CA certificate should be a trusted CA or has the resources to verify the CA. You can actually build a chain of CA certificates that lead to a trusted CA on top.
You must place the entire chain in the same file. This means your file contains content such as this example:
BEGIN CERTIFICATE ------ device certificate* END CERTIFICATE ------ BEGIN CERTIFICATE ------ intermediate CA certificate* END CERTIFICATE ------ BEGIN CERTIFICATE ------ Root CA certificate* END CERTIFICATE ------
How to Cause the Certificate to Match the URL
The WebAuth URL is set to 220.127.116.11 in order to authenticate yourself and the certificate is issued (this is the CN field of the WLC certificate). If you want to change the WebAuth URL to 'myWLC.com', for example, go into the virtual interface configuration (the 18.104.22.168 interface) and there you can enter a virtual DNS hostname, such as myWLC.com. This replaces the 22.214.171.124 in your URL bar. This name must also be resolvable. The sniffer trace shows how it all works, but when WLC sends the login page, WLC shows the myWLC.com address, and the client resolves this name with their DNS. This name should resolve as 126.96.36.199. This means that if you also use a name for the management of the WLC, you should use a different name for WebAuth. In other words, if you use myWLC.com mapped to the WLC management IP address, you must use a different name for the WebAuth, such as myWLCwebauth.com.
Troubleshoot Certificate Issues
This section explains how and what to check to troubleshoot certificate issues.
How to Check
You can download OpenSSL (for Windows, search for OpenSSL Win32) and install it. Without any configuration, you can go in the bin directory and try openssl s_client –connect www.mywebauthpage.com:443, if this URL is the URL where your WebAuth page is linked on your DNS. Refer to the "What to Check" section of this document for an example.
If your certificates use a private CA, you need to place the Root CA certificate in a directory on a local machine and use the openssl option -CApath. If you have an Intermediate CA, you must put it into the same directory as well.
In order to obtain general information about the certificate and to check it, use:
openssl x509 -in certificate.pem -noout -text
openssl verify certificate.pem
It might be also useful to convert certificates with the use of openssl:
openssl x509 -in certificate.der -inform DER -outform PEM -out certificate.pem
What to Check
You can see what certificates are sent to the client when it connects. Read the device certificate — the CN should be the URL where the web page is reachable. Read the “issued by” line of the device certificate. This must match the CN of the second certificate. Then this second certificate “issued by” must match the CN of the next certificate, and so on. Otherwise, it does not make a real chain. In the OpenSSL output shown here, you can see that openssl cannot verify the device certificate because its “issued by” does not match the name of the CA certificate provided.
Loading 'screen' into random state - done CONNECTED(00000760) depth=0 /O= <company>.ac.uk/OU=Domain Control Validated/CN=<company>.ac.uk verify error: num=20:unable to get local issuer certificate verify return:1 depth=0 /O= <company>.ac.uk/OU=Domain Control Validated/CN=<company>.ac.uk verify error: num=27:certificate not trusted verify return:1 depth=0 /O=<company>.ac.uk/OU= Domain Control Validated/CN=<company>.ac.uk verify error:num=21: unable to verify the first certificate verify return:1 --- Certificate chain 0 s:/O=<company>.ac.uk/OU= Domain Control Validated/CN=<company>.ac.uki:/C=US/ ST= Arizona/L=Scottsdale/O=.com/OU=http://certificates.gocompany.com/repository/CN= Secure Certification Authority/serialNumber=079 692871 s:/C=US/O=Company/OU=Class 2 Certification Authority i:/C=US/O=Company/OU=Class 2 Certification Authority --- Server certificate
BEGIN CERTIFICATE----- MIIE/zCCA+egAwIBAgIDRc2iMA0GCSqGSIb3DQEBBQUAMIHKMQswCQYDVQQGEwJV output cut* YMaj/NACviEU9J3iot4sfreCQSKkBmjH0kf/Dg1l0kmdSbc=
END CERTIFICATE----- subject=/O=<company>.ac.uk/OU=Domain Control Validated/CN=<company>c.ac.uk issuer=/C=US/ST=Arizona/L=Scottsdale/O=.com/OU=http://certificates. .com/repository/CN=Secure Certification Authority/serialNumber=0 7969287 --- No client certificate CA names sent --- SSL handshake has read 2476 bytes and written 322 bytes --- New, TLSv1/SSLv3, Cipher is AES256-SHA Server public key is 1024 bit Compression: NONE Expansion: NONE SSL-Session:
Key-Arg : None Start Time: 1220282986 Timeout : 300 (sec) Verify return code: 21 (unable to verify the first certificate) ---
Another possible issue is the certificate cannot be uploaded to the controller. In this situation there is no question of validity, CA, and so on. In order to verify this, you can first check the Trivial File Transfer Protocol (TFTP) connectivity and try to transfer a configuration file. Then, if you enter the debug transfer all enable command, you see that the problem is the installation of the certificate. This could be due to the wrong key used with the certificate. It could also be that the certificate is in a wrong format or is corrupted.
Cisco recommends that you compare the certificate content to a known, valid certificate. This allows you to see if a LocalkeyID attribute shows all 0s (already happened). If so, then the certificate should be reconverted. There are two commands with OpenSSL that allow you to return from .pem to .p12, and then reissue a .pem with the key of your choice.
Pre-step: If you received a .pem that contains a certificate followed by a key, copy/paste the key part: ----BEGIN KEY ---- until ------- END KEY ------ from the .pem into "key.pem".
openssl pkcs12 -export -in certificate.pem -inkey key.pem -out newcert.p12 ? You are prompted with a key; enter check123.
openssl pkcs12 -in newcert.p12 -out workingnewcert.pem -passin pass:check123 -passout pass:check123 This results in an operational .pem with the password check123.
Other Situations to Troubleshoot
Although mobility anchor has not been discussed in this document, if you are in an anchored guest situation, make sure the mobility exchange occurs correctly and that you see the client arrives on the anchor. Any further WebAuth problems need troubleshoot on the anchor.
Here are some common issues you can troubleshoot:
Users cannot associate to the guest WLAN.
This is not related to WebAuth. Check the client configuration, the security settings on the WLAN, if it is enabled, and whether radios are active and operative, and so on.
Users do not obtain IP address.
In a guest anchor situation, this is most often because the foreign and anchor was not configured exactly the same way. Otherwise, check the DHCP configuration, connectivity, and so on. Confirm whether or not other WLANs can use the same DHCP server without a problem. This still is not related to WebAuth.
User is not redirected to the login page.
This is the most common symptom, but is more precise. There are two possible scenarios.
The user is not redirected (user enters a URL and never reaches the WebAuth page). For this situation, check:
that a valid DNS server has been assigned to the client via DHCP (ipconfig /all),
that the user entered a valid URL in order to be redirected,
that the user went on an HTTP URL on port 80 (for example, to reach an ACS with http://localhost:2002 does not redirect you since you sent on port 2002 instead of 80).
The user is redirected to 188.8.131.52 correctly, but the page itself does not display.
This situation is most likely either a WLC problem (bug) or a client-side problem. It could be that the client has some firewall or blocking software or policy. It also could be that they have configured a proxy in their web browser.
Recommendation: Take a sniffer trace on the client PC. There is no need for special wireless software, only Wireshark, which runs on the wireless adapter and shows you if the WLC replies and tries to redirect. You have two possibilities: either there is no response from WLC, or something is wrong with the SSL handshake for the WebAuth page. For SSL handshake issue, you can check whether the user browser allows for SSLv3 (some only allow SSLv2), and if it is too aggressive on certificate verification.
It is a common step to manually enter http://184.108.40.206 in order to check if the web page appears without DNS. Actually, you can type http://220.127.116.11 and get the same effect. The WLC redirects any IP address you enter. Therefore, if you enter http://18.104.22.168, it does not make you work around the web redirection. If you enter https://22.214.171.124 (secure), this does not work because WLC does not redirect the HTTPS traffic (by default, this is actually possible in Version 8.0 and later). The best way to load the page directly without a redirect is to enter https://126.96.36.199/login.html.
Users cannot authenticate.
See the section of this document that discusses authentication. Check credentials locally on the RADIUS.
Users can successfully authenticate through WebAuth, but they do not have internet access afterwards.
You can remove WebAuth from the security of the WLAN, and then you should have an open WLAN. You can then try to access the web, the DNS and so on. If you experience issues there as well, remove WebAuth settings altogether and check your interfaces configuration.
You can use an HTTP proxy server. If you need the client to add an exception in its browser that 188.8.131.52 is not to go through the proxy server, you can make the WLC listen for HTTP traffic on the port of the proxy server (usually 8080).
In order to understand this scenario, you need to know what an HTTP proxy does. It is something you configure on the client side (IP address and port) in the browser.
The usual scenario when a user visits a website is to resolve the name to IP with DNS, and then it asks the web page to the web server. The process should always send the HTTP request for the page to the proxy. The proxy processes the DNS, if required, and forwards to the web server (if the page is not already cached on the proxy). The discussion is client-to-proxy only. Whether or not the proxy obtains the real web page is irrelevant to the client.
Here is the web authentication process:
User types in a URL.
Client PC sends to the Proxy server.
WLC intercepts and spoofs Proxy server IP; it replies to the PC with a redirect to 184.108.40.206.
At this stage, if the PC is not configured for it, it asks for the 220.127.116.11 WebAuth page to the proxy so it does not work. The PC must make an exception for 18.104.22.168; then it sends an HTTP request to 22.214.171.124 and proceeds with WebAuth. When authenticated, all communications go through proxy again. An exception configuration is usually in the browser close to the configuration of the proxy server. You should see the message: "Don't use proxy for those IP addresses".
With WLC Release 7.0 and later, the feature webauth proxy redirect can be enabled in the global WLC configuration options. When enabled, the WLC checks if the clients are configured to manually use a proxy. In that case, they redirect the client to a page that shows them how to modify their proxy settings to make everything work. The WebAuth proxy redirect can be configured to work on a variety of ports and is compatible with Central Web Authentication.
You can login on web authentication on HTTP instead of HTTPS. If you login on HTTP, you do not receive certificate alerts.
For earlier than WLC Release 7.2 code, you must disable HTTPS management of the WLC and leave HTTP management. However, this only allows the web management of the WLC over HTTP.
For WLC Release 7.2 code, use the config network web-auth secureweb disable command to disable. This only disables HTTPS for the web authentication and not the management. Note that this requires a reboot of the controller!
On WLC Release 7.3 and later code, you can enable/disable HTTPS for WebAuth only via GUI and CLI.