Using deploy time parameters in CDK 'codepipeline_actions.CloudFormationCreateUpdateStackAction'

I am clearly not understanding how dynamic parameters can be used when deploying a template in CodePipeline. Here is the basic scenario:

CodeBuild BUILD Action - Here I have retrieved, for instance, a value for COMMIT_NUMBER. This can be set as an environment variable, or saved to a file... whatever needs to be done. In a post_build step I package up the template using "sam package ...."

CloudFormation DEPLOY stage - Here I use

new codepipeline_actions.CloudFormationCreateUpdateStackAction({
      actionName: `The_Deploy`,
      templatePath: buildOutput.atPath(TEMPLATE_FILE_NAME),
      parameterOverrides, --These are known when I synth the pipeline
      stackName: envStackName,
      cfnCapabilities: [CfnCapabilities.AUTO_EXPAND, CfnCapabilities.ANONYMOUS_IAM],
      adminPermissions: true,
      role: buildRole,
      runOrder: runOrder || 1
    });

to deploy the template that was packaged up. In the props for this method, there is a parameterOverrides property, but anything in there would have to be known at build time.

My question is HOW do i set dynamic parameter values that are known in the build step, to the parameters consumed by the deploy step.

Thanks for any clarification!

Thank you @Ronan Cunningham, for the link : here. The KEY point that clarified how to do this was this sentence below, that I have not found explained well otherwise:

"Since namespaces are native CodePipeline feature, they are not restricted only to CloudFormation actions. Now you can for example define CodeBuild environment variables in a dynamic way as well (it is also possible to define export variables in CodeBuild - these values will will become step output values):" ....

To bring it all together here are the key pieces that allowed me to set an environment variable in the codebuild action and pass it to a cloudformation parameter IN CDK:

1.) add env variable and export variable in the build project

const buildProject = new codebuild.PipelineProject(construct, `buildProject`, {
    buildSpec: codebuild.BuildSpec.fromObject({
    version: '0.2',
    env: {
      "variables": {
        "MY_IMPORTANT_INFO": "some-default-value-here"
      },
      "exported-variables": [ "MY_IMPORTANT_INFO" ]
    },
    phases: {
      install: {...},
      build: {
        commands: [ NOTE... variable above can be changed here...]
      }
    },
    artifacts: {...}
    role: buildRole
  })

2.) Add namespace to the build action:

new codepipeline_actions.CodeBuildAction({
      actionName: `The_Build`,
      project: buildProject,
      input: sourceOutput,
      outputs: [buildOutput],
      role: buildRole,
      variablesNamespace: 'build'
    })

3.) In the deployment stage, I can now set the ParameterOverride by setting the parameter name to the environment variable that was exported in the build step:

new codepipeline_actions.CloudFormationCreateUpdateStackAction({
      actionName: `The_Deploy`,
      templatePath: buildOutput.atPath(TEMPLATE_FILE_NAME),
      parameterOverrides: [
        {"COMMIT_NUMBER": "#{build.MY_IMPORTANT_INFO}"}
      ],
      stackName: envStackName,
      cfnCapabilities: [CfnCapabilities.AUTO_EXPAND, CfnCapabilities.ANONYMOUS_IAM],
      adminPermissions: true,
      role: buildRole,
      runOrder: runOrder || 1
    });

Hallelujah!

And, thanks again to Ronan for the informative link!