diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9c087c2..bf6e7c9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@
 
 ## Changes since v7.5.1
 
+- [#2237](https://github.com/oauth2-proxy/oauth2-proxy/pull/2237) adds an option to append CA certificates (@emsixteeen)
 - [#2128](https://github.com/oauth2-proxy/oauth2-proxy/pull/2128) Update dependencies (@vllvll)
 - [#2274](https://github.com/oauth2-proxy/oauth2-proxy/pull/2274) Upgrade golang.org/x/net to v0.17.0 (@pierluigilenoci)
 - [#2282](https://github.com/oauth2-proxy/oauth2-proxy/pull/2282) Fixed checking Google Groups membership using Google Application Credentials (@kvanzuijlen)
diff --git a/docs/docs/configuration/alpha_config.md b/docs/docs/configuration/alpha_config.md
index a72dc63..8141f47 100644
--- a/docs/docs/configuration/alpha_config.md
+++ b/docs/docs/configuration/alpha_config.md
@@ -415,6 +415,7 @@ Provider holds all configuration for a single provider
 | `provider` | _[ProviderType](#providertype)_ | Type is the OAuth provider<br/>must be set from the supported providers group,<br/>otherwise 'Google' is set as default |
 | `name` | _string_ | Name is the providers display name<br/>if set, it will be shown to the users in the login page. |
 | `caFiles` | _[]string_ | CAFiles is a list of paths to CA certificates that should be used when connecting to the provider.<br/>If not specified, the default Go trust sources are used instead |
+| `useSystemTrustStore` | _bool_ | UseSystemTrustStore determines if your custom CA files and the system trust store are used<br/>If set to true, your custom CA files and the system trust store are used otherwise only your custom CA files. |
 | `loginURL` | _string_ | LoginURL is the authentication endpoint |
 | `loginURLParameters` | _[[]LoginURLParameter](#loginurlparameter)_ | LoginURLParameters defines the parameters that can be passed from the start URL to the IdP login URL |
 | `redeemURL` | _string_ | RedeemURL is the token redemption endpoint |
diff --git a/docs/docs/configuration/overview.md b/docs/docs/configuration/overview.md
index a362949..36848ca 100644
--- a/docs/docs/configuration/overview.md
+++ b/docs/docs/configuration/overview.md
@@ -154,6 +154,7 @@ An example [oauth2-proxy.cfg](https://github.com/oauth2-proxy/oauth2-proxy/blob/
 | `--prompt` | string | [OIDC prompt](https://openid.net/specs/openid-connect-core-1_0.html#AuthRequest); if present, `approval-prompt` is ignored | `""` |
 | `--provider` | string | OAuth provider | google |
 | `--provider-ca-file` |  string \| list |  Paths to CA certificates that should be used when connecting to the provider.  If not specified, the default Go trust sources are used instead. |
+| `--use-system-trust-store` | bool | Determines if `provider-ca-file` files and the system trust store are used. If set to true, your custom CA files and the system trust store are used otherwise only your custom CA files. | false |
 | `--provider-display-name` | string | Override the provider's name with the given string; used for the sign-in page | (depends on provider)                                            |
 | `--ping-path` | string | the ping endpoint that can be used for basic health checks | `"/ping"`                                                        |
 | `--ping-user-agent` | string | a User-Agent that can be used for basic health checks | `""` (don't check user agent)                                    |
diff --git a/pkg/apis/options/legacy_options.go b/pkg/apis/options/legacy_options.go
index 99be34b..1bb0610 100644
--- a/pkg/apis/options/legacy_options.go
+++ b/pkg/apis/options/legacy_options.go
@@ -507,6 +507,7 @@ type LegacyProvider struct {
 	ProviderType                       string   `flag:"provider" cfg:"provider"`
 	ProviderName                       string   `flag:"provider-display-name" cfg:"provider_display_name"`
 	ProviderCAFiles                    []string `flag:"provider-ca-file" cfg:"provider_ca_files"`
+	UseSystemTrustStore                bool     `flag:"use-system-trust-store" cfg:"use_system_trust_store"`
 	OIDCIssuerURL                      string   `flag:"oidc-issuer-url" cfg:"oidc_issuer_url"`
 	InsecureOIDCAllowUnverifiedEmail   bool     `flag:"insecure-oidc-allow-unverified-email" cfg:"insecure_oidc_allow_unverified_email"`
 	InsecureOIDCSkipIssuerVerification bool     `flag:"insecure-oidc-skip-issuer-verification" cfg:"insecure_oidc_skip_issuer_verification"`
@@ -561,6 +562,7 @@ func legacyProviderFlagSet() *pflag.FlagSet {
 	flagSet.String("provider", "google", "OAuth provider")
 	flagSet.String("provider-display-name", "", "Provider display name")
 	flagSet.StringSlice("provider-ca-file", []string{}, "One or more paths to CA certificates that should be used when connecting to the provider.  If not specified, the default Go trust sources are used instead.")
+	flagSet.Bool("use-system-trust-store", false, "Determines if 'provider-ca-file' files and the system trust store are used. If set to true, your custom CA files and the system trust store are used otherwise only your custom CA files.")
 	flagSet.String("oidc-issuer-url", "", "OpenID Connect issuer URL (ie: https://accounts.google.com)")
 	flagSet.Bool("insecure-oidc-allow-unverified-email", false, "Don't fail if an email address in an id_token is not verified")
 	flagSet.Bool("insecure-oidc-skip-issuer-verification", false, "Do not verify if issuer matches OIDC discovery URL")
@@ -659,6 +661,7 @@ func (l *LegacyProvider) convert() (Providers, error) {
 		ClientSecretFile:    l.ClientSecretFile,
 		Type:                ProviderType(l.ProviderType),
 		CAFiles:             l.ProviderCAFiles,
+		UseSystemTrustStore: l.UseSystemTrustStore,
 		LoginURL:            l.LoginURL,
 		RedeemURL:           l.RedeemURL,
 		ProfileURL:          l.ProfileURL,
diff --git a/pkg/apis/options/providers.go b/pkg/apis/options/providers.go
index 9599f23..8820f34 100644
--- a/pkg/apis/options/providers.go
+++ b/pkg/apis/options/providers.go
@@ -59,7 +59,9 @@ type Provider struct {
 	// CAFiles is a list of paths to CA certificates that should be used when connecting to the provider.
 	// If not specified, the default Go trust sources are used instead
 	CAFiles []string `json:"caFiles,omitempty"`
-
+	// UseSystemTrustStore determines if your custom CA files and the system trust store are used
+	// If set to true, your custom CA files and the system trust store are used otherwise only your custom CA files.
+	UseSystemTrustStore bool `json:"useSystemTrustStore,omitempty"`
 	// LoginURL is the authentication endpoint
 	LoginURL string `json:"loginURL,omitempty"`
 	// LoginURLParameters defines the parameters that can be passed from the start URL to the IdP login URL
diff --git a/pkg/util/util.go b/pkg/util/util.go
index a4425d9..0f3d70a 100644
--- a/pkg/util/util.go
+++ b/pkg/util/util.go
@@ -14,11 +14,40 @@ import (
 	"time"
 )
 
-func GetCertPool(paths []string) (*x509.CertPool, error) {
+func GetCertPool(paths []string, useSystemPool bool) (*x509.CertPool, error) {
 	if len(paths) == 0 {
 		return nil, fmt.Errorf("invalid empty list of Root CAs file paths")
 	}
-	pool := x509.NewCertPool()
+
+	var pool *x509.CertPool
+	if useSystemPool {
+		rootPool, err := getSystemCertPool()
+		if err != nil {
+			return nil, fmt.Errorf("unable to get SystemCertPool when append is true - #{err}")
+		}
+		pool = rootPool
+	} else {
+		pool = x509.NewCertPool()
+	}
+
+	return loadCertsFromPaths(paths, pool)
+
+}
+
+func getSystemCertPool() (*x509.CertPool, error) {
+	rootPool, err := x509.SystemCertPool()
+	if err != nil {
+		return nil, err
+	}
+
+	if rootPool == nil {
+		return nil, fmt.Errorf("SystemCertPool is empty")
+	}
+
+	return rootPool, nil
+}
+
+func loadCertsFromPaths(paths []string, pool *x509.CertPool) (*x509.CertPool, error) {
 	for _, path := range paths {
 		// Cert paths are a configurable option
 		data, err := os.ReadFile(path) // #nosec G304
diff --git a/pkg/util/util_test.go b/pkg/util/util_test.go
index b8eff50..167c3e5 100644
--- a/pkg/util/util_test.go
+++ b/pkg/util/util_test.go
@@ -190,7 +190,7 @@ func makeTestCertFile(t *testing.T, pem, dir string) *os.File {
 }
 
 func TestGetCertPool_NoRoots(t *testing.T) {
-	_, err := GetCertPool([]string(nil))
+	_, err := GetCertPool([]string(nil), false)
 	assert.Error(t, err, "invalid empty list of Root CAs file paths")
 }
 
@@ -204,34 +204,52 @@ func TestGetCertPool(t *testing.T) {
 		}
 	}(tempDir)
 
+	rootPool, _ := x509.SystemCertPool()
+	cleanPool := x509.NewCertPool()
+
+	tests := []struct {
+		appendCerts bool
+		pool        *x509.CertPool
+	}{
+		{false, cleanPool},
+		{true, rootPool},
+	}
+
 	certFile1 := makeTestCertFile(t, root1Cert, tempDir)
 	certFile2 := makeTestCertFile(t, root2Cert, tempDir)
 
-	certPool, err := GetCertPool([]string{certFile1.Name(), certFile2.Name()})
-	assert.NoError(t, err)
+	for _, tc := range tests {
+		// Append certs to "known" pool so we can compare them
+		assert.True(t, tc.pool.AppendCertsFromPEM([]byte(root1Cert)))
+		assert.True(t, tc.pool.AppendCertsFromPEM([]byte(root2Cert)))
 
-	cert1Block, _ := pem.Decode([]byte(cert1Cert))
-	cert1, _ := x509.ParseCertificate(cert1Block.Bytes)
-	assert.Equal(t, cert1.Subject.String(), cert1CertSubj)
+		certPool, err := GetCertPool([]string{certFile1.Name(), certFile2.Name()}, tc.appendCerts)
+		assert.NoError(t, err)
+		assert.True(t, tc.pool.Equal(certPool))
 
-	cert2Block, _ := pem.Decode([]byte(cert2Cert))
-	cert2, _ := x509.ParseCertificate(cert2Block.Bytes)
-	assert.Equal(t, cert2.Subject.String(), cert2CertSubj)
+		cert1Block, _ := pem.Decode([]byte(cert1Cert))
+		cert1, _ := x509.ParseCertificate(cert1Block.Bytes)
+		assert.Equal(t, cert1.Subject.String(), cert1CertSubj)
 
-	cert3Block, _ := pem.Decode([]byte(cert3Cert))
-	cert3, _ := x509.ParseCertificate(cert3Block.Bytes)
-	assert.Equal(t, cert3.Subject.String(), cert3CertSubj)
+		cert2Block, _ := pem.Decode([]byte(cert2Cert))
+		cert2, _ := x509.ParseCertificate(cert2Block.Bytes)
+		assert.Equal(t, cert2.Subject.String(), cert2CertSubj)
 
-	opts := x509.VerifyOptions{
-		Roots: certPool,
+		cert3Block, _ := pem.Decode([]byte(cert3Cert))
+		cert3, _ := x509.ParseCertificate(cert3Block.Bytes)
+		assert.Equal(t, cert3.Subject.String(), cert3CertSubj)
+
+		opts := x509.VerifyOptions{
+			Roots: certPool,
+		}
+
+		// "cert1" and "cert2" should be valid because "root1" and "root2" are in the certPool
+		// "cert3" should not be valid because "root3" is not in the certPool
+		_, err1 := cert1.Verify(opts)
+		assert.NoError(t, err1)
+		_, err2 := cert2.Verify(opts)
+		assert.NoError(t, err2)
+		_, err3 := cert3.Verify(opts)
+		assert.Error(t, err3)
 	}
-
-	// "cert1" and "cert2" should be valid because "root1" and "root2" are in the certPool
-	// "cert3" should not be valid because "root3" is not in the certPool
-	_, err1 := cert1.Verify(opts)
-	assert.NoError(t, err1)
-	_, err2 := cert2.Verify(opts)
-	assert.NoError(t, err2)
-	_, err3 := cert3.Verify(opts)
-	assert.Error(t, err3)
 }
diff --git a/pkg/validation/options.go b/pkg/validation/options.go
index a3ce051..8c80482 100644
--- a/pkg/validation/options.go
+++ b/pkg/validation/options.go
@@ -37,7 +37,7 @@ func Validate(o *options.Options) error {
 		}
 		http.DefaultClient = &http.Client{Transport: insecureTransport}
 	} else if len(o.Providers[0].CAFiles) > 0 {
-		pool, err := util.GetCertPool(o.Providers[0].CAFiles)
+		pool, err := util.GetCertPool(o.Providers[0].CAFiles, o.Providers[0].UseSystemTrustStore)
 		if err == nil {
 			transport := http.DefaultTransport.(*http.Transport).Clone()
 			transport.TLSClientConfig = &tls.Config{