[BUG] Error updating App spec: App Ingress authority routing only supports exact matching

[SantiColu]

Bug Report

Describe the bug

When updating a DigitalOcean App via Apps.Update, the API responds with:

Error 400. error validating app spec field "ingress.rules.rule.match.authority":
App Ingress authority routing only supports exact matching.

This happens even when the caller explicitly sets authority.exact = "", which is a valid value according to the DigitalOcean App Platform API and is accepted when sent as raw JSON.

The root cause is the following model definition in godo:

// AppIngressSpecRuleStringMatch The string match configuration.
type AppIngressSpecRuleStringMatch struct {
	// Prefix-based match. For example, `/api` will match `/api`, `/api/`, and any nested paths such as `/api/v1/endpoint`.
	Prefix string `json:"prefix,omitempty"`
	Exact  string `json:"exact,omitempty"`
}

Because Exact is a string with the omitempty tag, setting it to "" causes the field to be omitted during JSON marshaling, resulting in:

"authority": {}

Instead of the required:

"authority": {
  "exact": ""
}

This makes it impossible to send a valid App Spec using the typed godo structs when an empty exact authority match is required.

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Affected Resource(s)

• Apps (Apps.Update)

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Actual Behavior

• Calling Apps.Update with Authority.Exact = "" results in the exact field being omitted from the request payload.
• The DigitalOcean API rejects the request with a 400 validation error.
• There is no way to force "exact": "" using the current godo model definitions.

---

Expected Behavior

• Setting Authority.Exact = "" should result in "exact": "" being included in the marshaled JSON.
• It should be possible to express all valid DigitalOcean App Platform configurations using the provided godo structs, without requiring raw JSON or manual requests.

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Steps to Reproduce

1. Create or fetch an existing App with an ingress rule.
2. Set the ingress rule authority match to use an empty exact match:

   rule.Match.Authority.Exact = ""

3. Call:

   client.Apps.Update(ctx, appID, updateReq)

4. Observe the API response:

   Error 400. error validating app spec field "ingress.rules.rule.match.authority":
   App Ingress authority routing only supports exact matching.
   

---

Suggested Fix

Change the Exact field to allow explicit empty values, for example by:

• Removing omitempty from the Exact field tag, or
• Changing the type to *string and omitting omitempty, allowing callers to explicitly set an empty string.