RHDEVDOCS-5241: Added a module for custom parameter expansion

cicd/pipelines/using-pipelines-as-code.adoc

@@ -90,6 +90,8 @@ include::modules/op-using-repository-crd-with-pipelines-as-code.adoc[leveloffset
 
 include::modules/op-setting-concurrency-limits-in-repository-crd.adoc[leveloffset=+2]
 
+include::modules/op-custom-parameter-expansion.adoc[leveloffset=+2]
+
 include::modules/op-using-pipelines-as-code-resolver.adoc[leveloffset=+1]
 
 include::modules/op-using-remote-task-annotations-with-pipelines-as-code.adoc[leveloffset=+2]
@@ -135,4 +137,6 @@ include::modules/op-pipelines-as-code-command-reference.adoc[leveloffset=+1]
 
 * xref:../../cli_reference/tkn_cli/installing-tkn.adoc#installing-tkn[Installing tkn]
 
-* xref:../../cicd/pipelines/op-release-notes.adoc#op-release-notes[{pipelines-title} release notes]
+* xref:../../cicd/pipelines/op-release-notes.adoc#op-release-notes[{pipelines-title} release notes]
+
+* xref:../../applications/creating_applications/odc-creating-applications-using-developer-perspective.adoc#odc-creating-applications-using-the-developer-perspective[Creating applications using the Developer perspective]

modules/op-custom-parameter-expansion.adoc

@@ -0,0 +1,74 @@
+// This module is included in the following assembly:
+//
+// *cicd/pipelines/using-pipelines-as-code.adoc
+
+:_content-type: CONCEPT
+[id="op-custom-parameter-expansion_{context}"]
+= Custom parameter expansion
+
+You can use {pac} to expand a custom parameter within your `PipelineRun` resource by using the `params` field. You can specify a value for the custom parameter inside the template of the `Repository` custom resource (CR). The specified value replaces the custom parameter in your pipeline run.
+
+You can use custom parameters in the following scenarios:
+
+* To define a URL parameter, such as a registry URL that varies based on a push or a pull request.
+* To define a parameter, such as an account UUID that an administrator can manage without necessitating changes to the `PipelineRun` execution in the Git repository.
+
+[NOTE]
+====
+Use the custom parameter expansion feature only when you cannot use the Tekton `PipelineRun` parameters because Tekton parameters are defined in a `Pipeline` resource and customized alongside it inside a Git repository. However, custom parameters are defined and customized where the `Repository` CR is located. So, you cannot manage your CI/CD pipeline from a single point. 
+====
+
+The following example shows a custom parameter named `company` in the `Repository` CR:
+
+[source,yaml]
+----
+...
+spec:
+  params:
+    - name: company
+      value: "ABC Company"
+...
+----
+
+The value `ABC Company` replaces the parameter name `company` in your pipeline run and in the remotely fetched tasks.
+
+You can also retrieve the value for a custom parameter from a Kubernetes secret, as shown in the following example: 
+
+[source,yaml]
+----
+...
+spec:
+  params:
+    - name: company
+      secretRef:
+        name: my-secret
+        key: companyname
+...
+----
+
+{pac} parses and uses custom parameters in the following manner:
+
+* If you have a `value` and a `secretRef` defined, {pac} uses the `value`.
+* If you do not have a `name` in the `params` section, {pac} does not parse the parameter.
+* If you have multiple `params` with the same `name`, {pac} uses the last parameter.
+
+You can also define a custom parameter and use its expansion only when specified conditions were matched for a CEL filter. The following example shows a CEL filter applicable on a custom parameter named `company` when a pull request event is triggered:
+
+[source,yaml]
+----
+...
+spec:
+  params:
+    - name: company
+      value: "ABC Company"
+      filter:
+        - name: event
+          value: |
+      pac.event_type == "pull_request"
+...
+----
+
+[NOTE]
+====
+When you have multiple parameters with the same name and different filters, {pac} uses the first parameter that matches the filter. So, {pac} allows you to expand parameters according to different event types. For example, you can combine a push and a pull request event.
+====