diff --git a/cmd/onecli/run.go b/cmd/onecli/run.go
index e4445d9..7789d48 100644
--- a/cmd/onecli/run.go
+++ b/cmd/onecli/run.go
@@ -135,27 +135,57 @@ func (c *RunCmd) Run(out *output.Writer) error {
 	return nil
 }
 
-// writeGatewayCACert writes the gateway CA PEM to ~/.onecli/gateway-ca.pem.
-// Returns the path on success. Skips the write if on-disk content already matches.
-func writeGatewayCACert(pem string) (string, error) {
+// writeGatewayCACert writes a combined CA bundle (system CAs + gateway CA)
+// to ~/.onecli/ca-bundle.pem. Env vars like SSL_CERT_FILE REPLACE the
+// default trust store, so the bundle must include system root certificates
+// alongside the gateway CA.
+func writeGatewayCACert(gatewayPEM string) (string, error) {
 	home, err := os.UserHomeDir()
 	if err != nil {
 		return "", fmt.Errorf("resolving home dir: %w", err)
 	}
-	caPath := filepath.Join(home, ".onecli", "gateway-ca.pem")
+	caPath := filepath.Join(home, ".onecli", "ca-bundle.pem")
 	if err := os.MkdirAll(filepath.Dir(caPath), 0o700); err != nil {
 		return "", fmt.Errorf("creating CA dir: %w", err)
 	}
+
+	var buf bytes.Buffer
+	if systemCAs, err := readSystemCAs(); err == nil {
+		buf.Write(systemCAs)
+		if len(systemCAs) > 0 && systemCAs[len(systemCAs)-1] != '\n' {
+			buf.WriteByte('\n')
+		}
+	}
+	buf.WriteString(gatewayPEM)
+
+	combined := buf.Bytes()
 	existing, err := os.ReadFile(caPath)
-	if err == nil && bytes.Equal(existing, []byte(pem)) {
+	if err == nil && bytes.Equal(existing, combined) {
 		return caPath, nil
 	}
-	if err := os.WriteFile(caPath, []byte(pem), 0o600); err != nil {
-		return "", fmt.Errorf("writing CA cert: %w", err)
+	if err := os.WriteFile(caPath, combined, 0o600); err != nil {
+		return "", fmt.Errorf("writing CA bundle: %w", err)
 	}
 	return caPath, nil
 }
 
+var systemCAPaths = []string{
+	"/etc/ssl/cert.pem",                  // macOS
+	"/etc/ssl/certs/ca-certificates.crt", // Debian/Ubuntu
+	"/etc/pki/tls/certs/ca-bundle.crt",   // RHEL/Fedora/CentOS
+	"/etc/ssl/ca-bundle.pem",             // SUSE
+}
+
+func readSystemCAs() ([]byte, error) {
+	for _, p := range systemCAPaths {
+		data, err := os.ReadFile(p)
+		if err == nil && len(data) > 0 {
+			return data, nil
+		}
+	}
+	return nil, fmt.Errorf("no system CA bundle found")
+}
+
 // caTrustKeys are env vars we inject locally for CA trust. These aren't in
 // the server response but may exist in the parent env and need stripping.
 var caTrustKeys = []string{
diff --git a/internal/api/client.go b/internal/api/client.go
index 91fce3f..234c0f4 100644
--- a/internal/api/client.go
+++ b/internal/api/client.go
@@ -3,11 +3,14 @@ package api
 import (
 	"bytes"
 	"context"
+	"crypto/tls"
+	"crypto/x509"
 	"encoding/json"
 	"fmt"
 	"io"
 	"net/http"
 	"net/url"
+	"os"
 	"time"
 )
 
@@ -21,14 +24,33 @@ type Client struct {
 // New creates an API client.
 func New(baseURL, apiKey string) *Client {
 	return &Client{
-		baseURL: baseURL,
-		apiKey:  apiKey,
-		httpClient: &http.Client{
-			Timeout: 30 * time.Second,
-		},
+		baseURL:    baseURL,
+		apiKey:     apiKey,
+		httpClient: buildHTTPClient(),
 	}
 }
 
+func buildHTTPClient() *http.Client {
+	client := &http.Client{Timeout: 30 * time.Second}
+	f := os.Getenv("SSL_CERT_FILE")
+	if f == "" {
+		return client
+	}
+	data, err := os.ReadFile(f)
+	if err != nil {
+		return client
+	}
+	pool, err := x509.SystemCertPool()
+	if err != nil {
+		pool = x509.NewCertPool()
+	}
+	pool.AppendCertsFromPEM(data)
+	client.Transport = &http.Transport{
+		TLSClientConfig: &tls.Config{RootCAs: pool},
+	}
+	return client
+}
+
 // withProjectQuery appends a projectId query param to path when projectID is non-empty.
 func withProjectQuery(basePath, projectID string) string {
 	if projectID == "" {