feat: document LINE social sign-in provider

Relates to ory/kratos#4240

Author: David-Wobrock

docs/kratos/social-signin/98_line.mdx

@@ -0,0 +1,152 @@
+---
+id: line
+title: Add LINE as a social sign-in provider in Ory
+sidebar_label: LINE
+---
+
+# LINE
+
+```mdx-code-block
+import JsonnetWarning from "../../_common/jsonnetwarning.mdx"
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+<Tabs groupId="default">
+<TabItem value="console" label="Ory Console" default>
+
+Follow these steps to add LINE as a social sign-in provider to your project using the Ory Console:
+
+1. Go to <ConsoleLink route="project.socialSignIn" />.
+2. Click the switch next to the LINE logo to start the configuration.
+3. Copy the Redirect URI and save it for later use.
+
+</TabItem>
+<TabItem value="cli" label="Ory CLI">
+
+The default redirect URI for LINE is `https://$PROJECT_SLUG.projects.oryapis.com/self-service/methods/oidc/callback/line`. Write it down for later use.
+
+</TabItem>
+</Tabs>
+```
+
+Next you will need to create a LINE application and configure it to work with Ory. Here's how you can do that:
+
+1. Head over to the [LINE Business Account](https://account.line.biz/signup).
+2. Create a new channel [in the Developer Console](https://developers.line.biz/console/)
+3. Configure the required permissions: `PROFILE`, `OPENID_CONNECT`, `OC_EMAIL`.
+4. On the LINE Login tab, configure the Callback URLs.
+5. On the channel page, you will find the Channel ID and Channel Secret. Copy these values and save them for later use.
+
+LINE is now set up! Continue with the following steps in Ory Console or Ory CLI to complete the configuration:
+
+````mdx-code-block
+<Tabs groupId="default">
+<TabItem value="console" label="Ory Console" default>
+
+1. Copy the Channel ID and Channel Secret from the LINE Developer Console and paste them into the corresponding fields in the Ory Console.
+2. In the **Data Mapping** field of the form in the Ory Console, add the following Jsonnet code snippet,
+    which maps the desired claims to the Ory Identity schema:
+
+   ```jsonnet
+   local claims = std.extVar('claims');
+
+   {
+     identity: {
+       traits: {
+         [if 'email' in claims then 'email' else null]: claims.email,
+         email: claims.email,
+         [if "name" in claims then "first_name" else null]: claims.name,
+       },
+     },
+   }
+   ```
+
+```mdx-code-block
+   <JsonnetWarning format="Jsonnet code snippets" use="data mapping" />
+```
+
+10. Click **Save Configuration**.
+
+</TabItem>
+<TabItem value="cli" label="Ory CLI">
+1. Create a Jsonnet code snippet to map the desired claims to the Ory Identity schema.
+
+   ```jsonnet
+   local claims = std.extVar('claims');
+   {
+     identity: {
+       traits: {
+         [if 'email' in claims then 'email' else null]: claims.email,
+         email: claims.email,
+         [if "name" in claims then "first_name" else null]: claims.name,
+       },
+     },
+   }
+   ```
+
+```mdx-code-block
+   <JsonnetWarning format="Jsonnet code snippets" use="data mapping" />
+```
+
+4. Encode the Jsonnet snippet with [Base64](https://www.base64encode.org/) or host it under an URL accessible to Ory Network.
+
+   ```shell
+   cat your-data-mapping.jsonnet | base64
+   ```
+
+5. Download the Ory Identities config from your project and save it to a file:
+
+   ```shell
+   ## List all available workspaces
+   ory list workspaces
+
+   ## List all available projects
+   ory list projects --workspace <workspace-id>
+
+   ## Get config
+   ory get identity-config --project <project-id> --workspace <workspace-id> --format yaml > identity-config-$project-id.yaml
+   ```
+
+6. Add the social sign-in provider configuration to the downloaded config. Add the Jsonnet snippet with mappings as a Base64
+   string or provide an URL to the file.
+
+   ```yaml
+   selfservice:
+     methods:
+       oidc:
+         config:
+           providers:
+            - id: line
+              provider: line
+              auth_url: https://access.line.me/oauth2/v2.1/authorize
+              issuer_url: https://access.line.me
+              token_url: https://api.line.me/oauth2/v2.1/token
+              scope:
+                - profile
+                - email
+                - openid
+              client_id: .... # Replace this with the Channel ID
+              client_secret: .... # Replace this with the Channel Secret
+              mapper_url: "base64://{YOUR_BASE64_ENCODED_JSONNET_HERE}"
+              # Alternatively, use an URL:
+              # mapper_url: https://storage.googleapis.com/abc-cde-prd/9cac9717f007808bf17f22ce7f4295c739604b183f05ac4afb4
+         enabled: true
+   ```
+
+7. Update the Ory Identities configuration using the file you worked with:
+
+   ```shell
+   ory update identity-config --project <project-id> --workspace <workspace-id> --file identity-config.yaml
+   ```
+
+</TabItem>
+</Tabs>
+````
+
+## Troubleshooting
+
+```mdx-code-block
+import SocialSigninTroubleshooting from '../_common/social-sign-in-troubleshooting.mdx'
+
+<SocialSigninTroubleshooting />
+```