Using PowerShell to Post Channel Messages with Teams Workflows

Replacing the Incoming Webhook Connector with the Teams Post to Channel Workflow

Last week, I discussed the looming end in sight for Office 365 connectors following their retirement from SharePoint Online and Microsoft 365 Groups. Connectors are still supported to bring information into Teams channels and the incoming webhook connector is a popular choice to create posts in channels from different network sources. For instance, this article describes how to post a notification about a report about expiring Microsoft 365 groups while this article discusses how to post information about service degradation for Office 365 workloads.

Both articles show how to use PowerShell to format the information sent for posting to a channel through the incoming webhook connector. I wanted to do the same thing with Power Automate workflows, specifically with the workflow called Post to a channel when a webhook request is received, which seems very close in concept to the incoming webhook connector: both publish a public URL for information to be sent to, and both demand that the information is formatted in a certain way.

The problem I ran into is a dearth of knowledge about how to construct the request body with PowerShell to send to the workflow. I knew that an adaptive card is used, but the example in Microsoft’s documentation wasn’t a great starting point. But persistence pays and the examples of formatting cards for Teams are better, and the adaptive card designer helped to debug various elements. In the end, I had a solution, and here’s how it works.

Create the Workflow

Channels have a workflows option in their overflow […] menu. Go to the channel you want to use as the target for the notifications and select Workflows (Figure 1).

Select Post to a channel when a webhook request is received from the screen listing available workflow templates (Figure 2).

The workflow needs an account to authenticate connections and post to the channel (this is different to the incoming webhook connector, which doesn’t need to authenticate using an account). The account must be a member of the host team. If, like me, the organization uses a utility account for this kind of operation, you’ll need to add the account to the team or select one of the existing team members. Figure 3 shows that the utility account is selected and validated (green tick). If you want to use a different account, click the […] menu and choose another account to connect.

After collecting all the necessary information, the dialog displays the name of the target team and channel. You can choose a different team or channel at this point. Once the correct target is chosen, click Add workflow. Power Automate proceeds to create the workflow and responds with the workflow URI (Figure 4).

Copy the URL and keep it safe because it is needed to tell Power Automate where to post payloads. When a payload arrives, Power Automate parses its content and if it’s OK, posts the content to the target channel.

If you forget to copy the URI, you can find it by opening the Workflows app, selecting the workflow, and copying it from the When a Teams webhook request is received step (Figure 5). To avoid potential confusion if multiple workflows of the same type are in use, I suggest that you take the opportunity to rename the workflow to make its purpose obvious.

Posting Requests to the Workflow

It’s at this point that we do some PowerShell magic to create the request sent to the workflow URI. To create a realistic example, I decided to use the Get Service Health Graph API to retrieve the current health status for critical services running in the tenant, like Exchange Online, SharePoint Online, Teams, and so on.

The request is an adaptive card, which is composed of elements like text blocks, images, and fact set. I settled on a simple design composed of an image, a heading (text block), and a fact set. A fact has a name and a value. In this case, the name is a service (like “OneDrive for Business”) and the value is the current service health status (like “service degraded”).

I created a prototype adaptive card with indicators where to add the header and facts. Creating the facts is a matter of retrieving the service health status, filtering the data to extract the status for critical services, adding a graphic indicator for each depending on the health status. After generating the data, it was then a matter of formatting it in JSON to meet the requirements of the adaptive card schema and inserting the facts and header into the right places in the prototype adaptive card. The final step is to submit the request using the Invoke-MgGraphRequest cmdlet. Figure 6 shows the result.

You can download the script from GitHub.

Normal Migration Woes

I am no Power Automate expert and profess no insight into how Power Automate works behind the scenes. I approached this exercise from the perspective of a tenant administrator who needs to replace the incoming webhook connector with a workflow. Persistence, some experience with PowerShell, knowledge of how to navigate Microsoft documentation, and trial and error got me a result in a few hours.

Overall, the transition was harder than I expected, but that might be due to lack of knowledge. It’s always difficult to do things when you suffer from that problem. I’ll chalk the experience down to normal migration woes.

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