How to Connect Power Automate to a Custom .NET API

To connect Power Automate to a custom .NET API, build a Custom Connector using the API's OpenAPI definition and Entra ID OAuth for auth. Flows can then call your .NET endpoint securely, with no hardcoded credentials, and handle transient failures with a retry policy.

What you need before you start

This guide assumes the following are in place. Missing any one of these will stall you mid-setup.

• .NET 8 Web API deployed at an HTTPS endpoint. The API must be publicly accessible or reachable from Power Automate's cloud infrastructure via a firewall allowlist or Azure API Management.
• OpenAPI/Swagger definition. Swashbuckle (built into .NET 8 Web API templates) generates this at /swagger/v1/swagger.json.
• Azure AD / Entra ID tenant with app registration rights. You need permission to create app registrations and expose API scopes.
• Power Automate Premium license. Custom Connectors require a per-user Premium or per-flow plan. The standard Microsoft 365 license does not include them.
• Environment Maker role in the Power Platform environment where you will deploy the connector.
• Azure API Management (optional). Adds throttling, request logging, and a single front door if multiple flows share the same .NET API.

For background on connector concepts, browse our Power Automate and workflow automation guides.

Step-by-step: Connect Power Automate to a custom .NET API

1. Expose the .NET endpoint and confirm it returns clean JSON. In your .NET 8 Web API project, ensure the action method returns a typed response object so Swashbuckle documents it fully. Verify the generated OpenAPI definition at /swagger/v1/swagger.json accurately describes request parameters and response schema. Incomplete schema means Power Automate cannot generate typed connector inputs automatically.
2. Register the API in Azure AD (Entra ID) and require an access token. In the Azure Portal, go to App registrations and create a registration for your API. Under Expose an API, define an application ID URI and add a scope (for example, Invoke). In your .NET API, configure AddMicrosoftIdentityWebApi() and annotate protected endpoints with the required scope. Do not accept shared secrets in query strings or headers. They appear in logs and rotate poorly.
3. Create a second Entra ID app registration for the Power Automate connector. In App registrations, create a client application (for example, "MyAPI-PowerAutomate"). Under API permissions, grant it the scope from the previous step. Generate a client secret (note the expiry date; maximum is two years) or configure a certificate for longer-lived credentials. This registration is the identity Power Automate uses to request tokens.
4. Build a Custom Connector in Power Automate from the OpenAPI definition. In Power Automate, go to Data > Custom Connectors > New custom connector > Import an OpenAPI file. Upload the swagger.json. On the Security tab, select OAuth 2.0 and authorization type Azure Active Directory. Enter the client ID, client secret, tenant ID, and resource URL (the application ID URI from step 2). The Microsoft Custom Connectors documentation has a full field reference.
5. Test a single connector operation in the test console. On the Test tab, create a new connection using the OAuth credentials and run one operation with sample input. Confirm the response matches the expected schema. If the token request fails, check that the redirect URI in Entra ID matches Power Automate's OAuth callback URL shown on the Security tab.
6. Use the connector in a flow and configure error handling and retry policy. Add the Custom Connector action to a flow and map its typed inputs from upstream steps. In the action settings (three-dot menu > Settings), set a Retry Policy using Fixed Interval with count 3 and interval 20 seconds. Wrap the action in a Scope container and add a Configure run after branch for failed and timed-out outcomes so a transient 500 does not terminate the entire flow run.

Authentication options and when to use each

Client secrets are the fastest way to get a connector working, but they expire (Entra ID caps secrets at two years). Certificates do not expire on the same schedule and are auditable in Azure Key Vault. Azure API Management is worth adding when multiple teams' flows call the same .NET API and you want rate-limiting, request logging, or IP restrictions applied at the gateway rather than in application code.

Start with Entra ID OAuth 2.0 and a client secret. Move to certificate auth or APIM if the connector is shared across teams or if the API handles data subject to audit requirements.

Where this gets tricky

Three patterns break this setup in production:

Hardcoded API key instead of Entra ID auth. Passing a shared secret in a custom header works until the key leaks, rotates under pressure, or the security team audits the flow. Custom Connector credentials stored in Entra ID are scoped, auditable in Azure logs, and do not live inside the flow definition where any Maker with read access can see them.

Calling the API inside an Apply to Each loop without batching. A flow iterating over 500 records that calls your .NET API once per item will hit Power Automate's action throttling limits and your API's rate limits at the same time. Design the .NET endpoint to accept an array of inputs, or enable Apply to Each concurrency control to cap parallel calls at a value your API can handle.

No retry policy on transient failures. Power Automate's default behavior when an action fails is to fail the run. A .NET API returning a 500 due to a database blip or a brief network interruption will terminate the flow unless you configure a retry policy before go-live, not after the first production incident.

How QServices can help

QServices builds Power Automate integrations against custom .NET APIs as part of our Power Automate development service. Most connector builds run 3 to 8 weeks end-to-end. Project budgets range from $6,000 for a single-connector project to $35,000 for multi-flow automation replacing a manual process. For a detailed breakdown, see our Power Automate cost guide.

We have shipped this integration pattern in production. For a manufacturing client, we built Power Apps and .NET integrations that digitized the full inventory lifecycle, including supervisor approval workflows tied to a custom ERP API:

For a US pest control business, we connected a .NET API to QuickBooks Online, automating customer and invoice syncing and eliminating manual invoicing errors that were causing billing delays:

Do I need a Premium Power Automate license to use a Custom Connector?

Yes. Custom Connectors are a premium feature in Power Automate. You need either a Power Automate Premium per-user plan or a per-flow plan assigned to the flow that uses the connector. The standard Microsoft 365 or Office 365 license does not include Custom Connector access. Verify your license in the Power Platform admin center before starting the build to avoid discovering the restriction after completing the setup.