Resolve "Docs: Post-merge troubleshooting review"

doc/user/group/saml_sso/index.md

@@ -42,7 +42,8 @@ GitLab.com uses the SAML NameID to identify users. The NameID element:
 - Is case sensitive. The NameID must match exactly on subsequent login attempts, so should not rely on user input that could change between upper and lower case.
 - Should not be an email address or username. We strongly recommend against these as it is hard to guarantee they will never change, for example when a person's name changes. Email addresses are also case-insensitive, which can result in users being unable to sign in.
 
-The recommended field for supported providers are in the [provider specific notes](#providers).
+The relevant field name and recommended value for supported providers are in the [provider specific notes](#providers).
+appropriate corresponding field.
 
 CAUTION: **Warning:**
 Once users have signed into GitLab using the SSO SAML setup, changing the `NameID` will break the configuration and potentially lock users out of the GitLab group.
@@ -407,11 +408,13 @@ If you do not wish to use that GitLab user with the SAML login, you can [unlink
 
 ### Message: "SAML authentication failed: User has already been taken"
 
-The user you are signed in with already has SAML linked to a different identity. This might mean you've attempted to link multiple SAML identities to the same user for a given Identity Provider. This could also be a symptom of the Identity Provider returning an inconsistent [NameID](#nameid).
+The user that you're signed in with already has SAML linked to a different identity.
+Here are possible causes and solutions:
 
-To change which identity you sign in with, you can [unlink the previous SAML identity](#unlinking-accounts) from this GitLab account.
-
-Alternatively, an admin of your Identity Provider can use the [SCIM API](../../../api/scim.md) to update your `extern_uid` to match the current **NameID**.
+| Cause                                                                                          | Solution                                                                                                                                                                    |
+|------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| You've tried to link multiple SAML identities to the same user, for a given Identity Provider. | Change the identity that you sign in with. To do so, [unlink the previous SAML identity](#unlinking-accounts) from this GitLab account before attempting to sign in again. |
+| The Identity Provider might be returning an inconsistent [NameID](#nameid).                    | Ask an admin of your Identity Provider to use the [SCIM API](../../../api/scim.md) to update your `extern_uid` to match the current **NameID**.                             |
 
 ### Message: "SAML authentication failed: Email has already been taken"
 
@@ -427,13 +430,13 @@ This can be prevented by configuring the [NameID](#nameid) to return a consisten
 
 ### The NameID has changed
 
-As mentioned in the [NameID](#nameid) section, if the NameID changes for any user, the user can be locked out. This is common for setups using an email address as the identifier.
-
-To fix the issue, follow the steps outlined in the ["SAML authentication failed: User has already been taken"](#message-saml-authentication-failed-user-has-already-been-taken) section. We recommend using the API method if many users are affected so that the changes can be done in a scripted batch.
+| Cause                                                                                                                                                                                     | Solution                                                                                                                                                                                                                                           |
+|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| As mentioned in the [NameID](#nameid) section, if the NameID changes for any user, the user can be locked out. This is a common problem when an email address is used as the identifier. | Follow the steps outlined in the ["SAML authentication failed: User has already been taken"](#message-saml-authentication-failed-user-has-already-been-taken) section. If many users are affected, we recommend that you use the appropriate API. |
 
 ### I need to change my SAML app
 
-Users need to [unlink the previous SAML identity](#unlinking-accounts) and [link their identity](#user-access-and-management) using the new SAML app.
+Users will need to [unlink the current SAML identity](#unlinking-accounts) and [link their identity](#user-access-and-management) to the new SAML app.
 
 ### My identity provider isn't listed
 

doc/user/group/saml_sso/scim_setup.md

@@ -167,7 +167,10 @@ As a workaround, try an alternate mapping:
 
 ### Message: "SAML authentication failed: Email has already been taken"
 
-It is expected for the app's logs to show this error for any existing user until they sign in for the first time. GitLab will not allow multiple accounts to have the same email address.
+This message may be caused by the following:
+
+- Existing users have not yet signed into the new app.
+- The identity provider attempts to create a new user account in GitLab with an email address that already exists in GitLab.com.
 
 ### How do I diagnose why a user is unable to sign in
 
@@ -197,15 +200,17 @@ Whether the value was changed or you need to map to a different field, ensure `i
 
 If GitLab's `externalId` doesn't match the SAML NameId, it will need to be updated in order for the user to log in. Ideally your identity provider will be configured to do such an update, but in some cases it may be unable to do so, such as when looking up a user fails due to an ID change.
 
-Fixing the fields your SCIM identity provider sends as `id` and `externalId` can correct this, however we use these IDs to look up users so if the identity provider is unaware of the current values for these it may try to create new duplicate users instead.
-
-If the `externalId` we have stored for a user has an incorrect value that doesn't match the SAML NameId, then it can be corrected ine on or two ways.
-
-One option is to have users can be delinked and relink following details in the ["SAML authentication failed: User has already been taken"](./index.md#message-saml-authentication-failed-user-has-already-been-taken) section. Additionally, to unlink all users at once, remove all users from the SAML app while SCIM is still turned on.
+Be cautious if you revise the fields used by your SCIM identity provider, typically `id` and `externalId`.
+We use these IDs to look up users. If the identity provider does not know the current values for these fields,
+that provider may create duplicate users.
 
-Another option is with the manual use of the SCIM API.
+If the `externalId` for a user is not correct, and also doesn't match the SAML NameID,
+you can address the problem in the following ways:
 
-The [SCIM API](../../../api/scim.md#update-a-single-saml-user) can be used to manually correct the `externalId` stored for users so that it matches the SAML NameId. You'll need to know the desired value that matches the `NameId` as well as the current `externalId` to look up the user.
+- You can have users unlink and relink themselves, based on the ["SAML authentication failed: User has already been taken"](./index.md#message-saml-authentication-failed-user-has-already-been-taken) section.
+- You can unlink all users simultaneously, by removing all users from the SAML app while provisioning is turned on.
+- You can use the [SCIM API](../../../api/scim.md#update-a-single-saml-user) to manually correct the `externalId` stored for users to match the SAML `NameId`.
+  To look up a user, you'll need to know the desired value that matches the `NameId` as well as the current `externalId`.
 
 It is then possible to issue a manual SCIM#update request, for example: