Keychain Credentials Update (#695)

* Keychain Credentials Update

Contains new content and screenshots on what a keychain credential is and how to use one.

* remove new yarn stuff

* run format

* create a ____, is sub to Keychain Credentials

* wording

---------

Co-authored-by: Taylor Downs <[email protected]>

Author: theroinaochieng

docs/manage-projects/manage-credentials.md

@@ -6,7 +6,7 @@ You can view the Credentials related to a Project under the Project
 `Settings > Credentials` page. In this article, you'll learn how to manage your
 credentials related to a project.
 
-### View all Project Credentials
+## View all Project Credentials
 
 Via this `Credentials` page, you can see a list of all Credentials, including
 the name, type, and owner, and whether they are for a production environment.
@@ -21,7 +21,7 @@ etc.).
 
 :::
 
-### Create a new Credential
+## Create a new Credential
 
 1. Click on the `New Credential` button, and choose the type of app you want to
    connect.
@@ -53,13 +53,101 @@ ask on [Community](https://community.openfn.org).
 
 ![New Credential Ready](/img/lightning_new_cred_ready.webp)
 
-### Share Credentials
+## Keychain Credentials (Variable Auth)
+
+Keychain credentials allow for a single job to make use of multiple credentials.
+They work by inspecting the data in the job's runtime state (i.e., state.data)
+and checking for the value of a predetermined identifier. Based on that value,
+present in the data for a given source message, for example, another credential
+will be selected and applied for that particular job run.
+
+Keychain credentials allow for a single job to make use of multiple credentials.
+They work by inspecting the data in the initial input for a given run (e.g.,
+state.data) and checking for the value of a predetermined identifier.
+
+Imagine you have 2 credentials in your project:
+
+1. Taylor’s Login, External ID: abc123, Body:
+   `{ username: “tay”, password: “shhhhh” }`
+
+2. Roina’s Login, External ID: def456, Body:
+   `{ username: “ro”, password: “veryshh” }`
+
+And a job that uses a “Keychain Credential” with a path of `$.data.myId`.
+
+If a job in your workflow uses the “Keychain Credential” and the initial
+dataclip for a given run looks like this:
+
+```json
+{
+  "data": {
+    "content": "Hello world",
+    "myId": "abc123"
+  }
+}
+```
+
+Then the keychain credential will search for abc123 in your project credentials
+and provide those secrets to the same job. I.e., the will run with the “Taylor’s
+Login” credential.
+
+If another run is executed, and the initial dataclip for that run is:
+
+```json
+{
+  "data": {
+    "content": "Goodbye!",
+    "myId": "def456"
+  }
+}
+```
+
+The same job will run with the “Roina’s Login” credential.
+
+:::info Notes & Limitations
+
+Since credential secrets are fetched at the start of a run (not the start of a
+step) it’s not currently possible to resolve keychain credentials based on data
+that is added to state later in a run. I.e., the data must be present in the
+input dataclip for the whole run, not the input dataclip of the step that uses
+the keychain credential.
+
+:::
+
+### Create a Keychain Credential
+
+1. On the `Credentials` page under project settings, click on the dropdown icon
+   on the `Add New` button to select the Keychain option:
+   
+   ![](/img/keychain_credential_dropdown.webp)
+
+2. Name your keychain credential and assign it a JSONPath expression. You can
+   also select a default credential to use when the JSONPath expression doesn't
+   match:
+   
+   ![](/img/keychain_modal.webp)
+
+3. Assign an external ID for your keychain to access by creating a new
+   credential or editing an existing credential:
+   
+   ![](/img/assign_externalID.webp)
+
+4. Now on a job in your workflow, you are able to select and use a keychain
+   credential:
+   
+   ![](/img/keychain_selection.webp)
+
+5. You can now reference your keychain in your input to use it:
+   
+   ![](/img/keychain_input.webp)
+
+## Share Credentials
 
 If you own a Credential, you can choose which Project has access to it. To
 update which Projects your Credential is shared with, follow the steps on the
 [User Credentials docs page](/documentation/user-credentials).
 
-### `Raw JSON` Credentials
+## `Raw JSON` Credentials
 
 Raw credentials are valid JSON documents which are passed into a job's runtime
 state. Note that owners of these credentials will be able to view them, in their