VERCEL: Fix some bugs (#3887)

The PR follows https://github.com/StackExchange/dnscontrol/pull/3542

Found some bugs when running intergration tests locally again, and the
PR is an attempt to fix them:

- When updating/creating HTTPS/SRV records, Vercel API only reads from
the corresponding struct (either `srv` or `https`). If we provide a
`value`, the Vercel API will reject with an error.
- The PR makes `Value` "nil-able", and sets `Value` to nil when dealing
with `SRV` or `HTTPS` records.
- When updating a record, currently, we treat the empty SVC param as
omitting the field. But with Vercel's API, omitting a field means not
updating the field. We need to explicitly make the field an empty string
to create/update an empty SVC param, and the PR does that.
- Vercel implements an unknown `ech=` parameter validation process for
HTTPS records. The validation process is unknown, undocumented, thus I
can't implement a `rejectif` for `AuditRecord`.
- Let's make this a known caveat, describe it in the provider docs, skip
these intergration tests, and move on.

Please tag this PR w/ `provider-VERCEL`.

documentation/provider/vercel.md

@@ -144,3 +144,13 @@ Vercel does not allow the record type to be changed after creation. If you try t
 ### Minimum TTL
 
 Vercel enforces a minimum TTL of 60 seconds (1 minute) for all records. We will always silently override the TTL to 60 seconds if you try to set a lower TTL.
+
+### HTTPS Record ECH Base64 Validation
+
+Currently, Vercel does implements IETF's "Bootstrapping TLS Encrypted ClientHello with DNS Service Bindings" draft. However, Vercel also implements a validation process for the `ech` parameter in the `HTTPS` records, and will reject the request with the following error message if Vercel considers the `ech` value is invalid:
+
+```
+Invalid base64 string: [input] (key: ech)
+```
+
+The detail of Vercel's validation process is unknown, thus we can not support static validation for `dnscontrol check` or `dnscontrol preview`. You should use `ech=` with caution.

integrationTest/integration_test.go

@@ -292,6 +292,18 @@ func makeTests() []*TestGroup {
 
 		testgroup("Ech",
 			requires(providers.CanUseHTTPS),
+			not(
+				// Last tested in 2025-12-04. Turns out that Vercel implements an unknown validation
+				// on the `ech` parameter, and our dummy base64 string are being rejected with:
+				//
+				// Invalid base64 string: [our base64] (key: ech)
+				//
+				// Since Vercel's validation process is unknown and not documented, we can't implement
+				// a rejectif within auditrecord to reject them statically.
+				//
+				// Let's just ignore ECH test for Vercel for now.
+				"VERCEL",
+			),
 			tc("Create a HTTPS record", https("@", 1, "example.com.", "alpn=h2,h3")),
 			tc("Add an ECH key", https("@", 1, "example.com.", "alpn=h2,h3 ech=some+base64+encoded+value///")),
 			tc("Ignore the ECH key while changing other values", https("@", 1, "example.net.", "port=80 ech=IGNORE")),

providers/vercel/api.go

@@ -89,12 +89,13 @@ func (c *vercelProvider) ListDNSRecords(ctx context.Context, domain string) ([]D
 type httpsRecord struct {
 	Priority int64  `json:"priority"`
 	Target   string `json:"target"`
-	Params   string `json:"params,omitempty"`
+	Params   string `json:"params"`
 }
 
 // createDNSRecordRequest embeds the official SDK request but adds HTTPS support
 type createDNSRecordRequest struct {
 	vercelClient.CreateDNSRecordRequest
+	Value *string      `json:"value,omitempty"`
 	HTTPS *httpsRecord `json:"https,omitempty"`
 }
 

providers/vercel/vercelProvider.go

@@ -317,7 +317,7 @@ func toVercelCreateRequest(domain string, rc *models.RecordConfig) (createDNSRec
 	}
 	req.Name = name
 	req.Type = rc.Type
-	req.Value = rc.GetTargetField()
+	req.Value = ptrString(rc.GetTargetField())
 	req.TTL = int64(rc.TTL)
 	req.Comment = ""
 
@@ -331,17 +331,24 @@ func toVercelCreateRequest(domain string, rc *models.RecordConfig) (createDNSRec
 			Port:     int64(rc.SrvPort),
 			Target:   rc.GetTargetField(),
 		}
-		req.Value = "" // SRV uses the SRV struct, not Value
+		// When dealing with SRV records, we must not set the Value fields,
+		// otherwise the API throws an error:
+		// bad_request - Invalid request: should NOT have additional property `value`
+		req.Value = nil
 	case "TXT":
-		req.Value = rc.GetTargetTXTJoined()
+		req.Value = ptrString(rc.GetTargetTXTJoined())
 	case "HTTPS":
 		req.HTTPS = &httpsRecord{
 			Priority: int64(rc.SvcPriority),
 			Target:   rc.GetTargetField(),
 			Params:   rc.SvcParams,
 		}
+		// When dealing with HTTPS records, we must not set the Value fields,
+		// otherwise the API throws an error:
+		// bad_request - Invalid request: should NOT have additional property `value`.
+		req.Value = nil
 	case "CAA":
-		req.Value = fmt.Sprintf(`%v %s "%s"`, rc.CaaFlag, rc.CaaTag, rc.GetTargetField())
+		req.Value = ptrString(fmt.Sprintf(`%v %s "%s"`, rc.CaaFlag, rc.CaaTag, rc.GetTargetField()))
 	}
 
 	return req, nil
@@ -373,7 +380,10 @@ func toVercelUpdateRequest(rc *models.RecordConfig) (updateDNSRecordRequest, err
 			Port:     ptrInt64(int64(rc.SrvPort)),
 			Target:   &value,
 		}
-		req.Value = nil // SRV uses the SRV struct, not Value
+		// When dealing with SRV records, we must not set the Value fields,
+		// otherwise the API throws an error:
+		// bad_request - Invalid request: should NOT have additional property `value`
+		req.Value = nil
 	case "TXT":
 		txtValue := rc.GetTargetTXTJoined()
 		req.Value = &txtValue
@@ -383,6 +393,10 @@ func toVercelUpdateRequest(rc *models.RecordConfig) (updateDNSRecordRequest, err
 			Target:   rc.GetTargetField(),
 			Params:   rc.SvcParams,
 		}
+		// When dealing with HTTPS records, we must not set the Value fields,
+		// otherwise the API throws an error:
+		// bad_request - Invalid request: should NOT have additional property `value`.
+		req.Value = nil
 	case "CAA":
 		value := fmt.Sprintf(`%v %s "%s"`, rc.CaaFlag, rc.CaaTag, rc.GetTargetField())
 		req.Value = &value
@@ -395,3 +409,7 @@ func toVercelUpdateRequest(rc *models.RecordConfig) (updateDNSRecordRequest, err
 func ptrInt64(v int64) *int64 {
 	return &v
 }
+
+func ptrString(v string) *string {
+	return &v
+}