Add missing cilogon troubleshoot doc from prev PR

docs/howto/troubleshoot/cilogon-user-accounts.md

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+# CILogon: switch Identity Providers or user accounts
+
+By default, logging in with a particular user account will persist your credentials in future sessions.
+This means that you'll automatically re-use the same institutional and user account when you access the hub's home page.
+
+## Switch Identity Providers
+
+1. **Logout of the Hub** using the logout button or by going to `https://{hub-name}/hub/logout`.
+2. **Clear browser cookies** (optional). If the user asked CILogon to re-use the same Identity Provider connection when they logged in, they'll need to [clear browser cookies](https://www.lifewire.com/how-to-delete-cookies-2617981) for <https://cilogon.org>.
+
+   ```{figure} ../../images/cilogon-remember-this-selection.png
+   The dialog box that allows you to re-use the same Identity Provider.
+   ```
+
+   Firefox example:
+   ```{figure} ../../images/cilogon-clear-cookies.png
+   An example of clearing cookies with Firefox.
+   ```
+
+3. The next time the user goes to the hub's landing page, they'll be asked to re-authenticate and will be presented with the list of available Identity Providers after choosing the CILogon connection.
+4. They can now choose **another Identity Provider** via CILogon.
+
+```{note}
+If the user choses the same Identity Provider, then they will be automatically logged in with the same user account they've used before. To change the user account, see [](troubleshoot:cilogon:switch-user-accounts).
+```
+
+(troubleshoot:cilogon:switch-user-accounts)=
+## Switch user accounts
+
+1. Logout of the Hub using the logout button or by going to `https://{hub-name}/hub/logout`.
+2. Logout of CILogon by going to the [CILogon logout page](https://cilogon.org/logout).
+3. The next time the user goes to the hub's landing page, they'll be asked to re-authenticate and will be presented with the list of available Identity Providers after choosing the CILogon connection.
+4. Choose the **same Identity Provider** to login.
+5. The user can now choose **another user account** to login with.
+
+# 403 - Unauthorized errors
+
+If you see a 403 error page, this means that the account you were using to login hasn't been allowed by the hub administrator.
+
+```{figure} ../../images/403-forbidden.png
+```
+
+If you think this is an error, and the account should have been allowed, then contact the hub adminstrator/s.
+
+If you used the wrong user account, you can log in using another account by following the steps in [](troubleshoot:cilogon:switch-user-accounts).