diff --git a/README.md b/README.md
index e346dc1..5b4d808 100644
--- a/README.md
+++ b/README.md
@@ -57,11 +57,13 @@ Runtime configuration options:
 
 * `authorized_principals` - string, comma separated list of authorized principals, default `""`.
   If set, the user needs to have a principal in this list in order to use this module. If
-  this and `authorized_principals_file` are both set, only the last option listed is checked.
+  this and `authorized_principals_file` or `authorized_principals_command` are set, only the last option listed is checked.
 
 * `authorized_principals_file` - string, path to an authorized_principals file, default `""`.
   If set, users need to have a principal listed in this file in order to use this module.
-  If this and `authorized_principals` are both set, only the last option listed is checked.
+  If this and `authorized_principals` or `authorized_principals_command` are set, only the last option listed is checked.
+
+* `authorized_principals_command` - string, absolute path to a program that generates a list of valid principals. If set, users need to have a principal generated by this program in order to use this module. If this and `authorized_principals` or `authorized_principals_file` are set, only the last option is checked.
 
 * `group` - string, default, `""`
   If set, the user needs to be a member of this group in order to use this module.
diff --git a/pam_ussh.go b/pam_ussh.go
index 11ce4d0..3b2ea91 100644
--- a/pam_ussh.go
+++ b/pam_ussh.go
@@ -34,6 +34,7 @@ import (
 	"log/syslog"
 	"net"
 	"os"
+	"os/exec"
 	"path"
 	"runtime"
 	"strings"
@@ -155,7 +156,16 @@ func authenticate(w io.Writer, uid int, username, ca string, principals map[stri
 			continue
 		}
 
-		if err := c.CheckCert(username, cert); err != nil {
+		// If a manual set of principals is provided, don't require
+		// the username to be in the certificate's principals
+		// Principals are verified at the end of this function
+		testedPrincipal := username
+		if len(principals) > 0 && len(cert.ValidPrincipals) > 0 {
+			testedPrincipal = cert.ValidPrincipals[0]
+		}
+
+		if err := c.CheckCert(testedPrincipal, cert); err != nil {
+			pamLog("Error validating cert: %v\n", err)
 			continue
 		}
 
@@ -216,6 +226,19 @@ func loadValidPrincipals(principals string) (map[string]struct{}, error) {
 	return p, nil
 }
 
+func executePrincipalsCommand(command string) (map[string]struct{}, error) {
+	args := strings.Split(command, " ")
+	out, err := exec.Command(args[0], args[1:]...).Output()
+	if err != nil {
+		return nil, err
+	}
+	p := make(map[string]struct{})
+	for _, principal := range strings.Split(strings.TrimSpace(string(out)), "\n") {
+		p[principal] = struct{}{}
+	}
+	return p, nil
+}
+
 func pamAuthenticate(w io.Writer, uid int, username string, argv []string) AuthResult {
 	runtime.GOMAXPROCS(1)
 
@@ -243,6 +266,13 @@ func pamAuthenticate(w io.Writer, uid int, username string, argv []string) AuthR
 				return AuthError
 			}
 			authorizedPrincipals = ap
+		case "authorized_principals_command":
+			ap, err := executePrincipalsCommand(opt[1])
+			if err != nil {
+				pamLog("%v", err)
+				return AuthError
+			}
+			authorizedPrincipals = ap
 		default:
 			pamLog("unkown option: %s\n", opt[0])
 		}
diff --git a/pam_ussh_test.go b/pam_ussh_test.go
index 50decde..331999d 100644
--- a/pam_ussh_test.go
+++ b/pam_ussh_test.go
@@ -51,6 +51,18 @@ func TestLoadPrincipals(t *testing.T) {
 		require.True(t, ok)
 	})
 }
+func TestExecutePrincipalCommand(t *testing.T) {
+	WithTempDir(func(dir string) {
+		p := path.Join(dir, "script")
+		e := ioutil.WriteFile(p, []byte("#!/bin/bash\necho \"test\""), 0755)
+		require.NoError(t, e)
+
+		r, e := executePrincipalsCommand(p)
+		require.NoError(t, e)
+		_, ok := r["test"]
+		require.True(t, ok)
+	})
+}
 
 func TestNoAuthSock(t *testing.T) {
 	oldAgent := os.Getenv("SSH_AUTH_SOCK")
@@ -109,6 +121,7 @@ func TestPamAuthorize(t *testing.T) {
 		ca := path.Join(dir, "ca")
 		caPamOpt := fmt.Sprintf("ca_file=%s", ca)
 		principals := path.Join(dir, "principals")
+		principalsCommand := path.Join(dir, "principalsCommand")
 
 		k, e := rsa.GenerateKey(rand.Reader, 1024)
 		require.NoError(t, e)
@@ -125,6 +138,9 @@ func TestPamAuthorize(t *testing.T) {
 		e = ioutil.WriteFile(principals, []byte("group:foober"), 0444)
 		require.NoError(t, e)
 
+		e = ioutil.WriteFile(principalsCommand, []byte("#!/bin/bash\necho 'foober'"), 0755)
+		require.NoError(t, e)
+
 		WithSSHAgent(func(a agent.Agent) {
 			a.Add(agent.AddedKey{PrivateKey: userPriv, Certificate: c})
 
@@ -156,6 +172,23 @@ func TestPamAuthorize(t *testing.T) {
 			r = pamAuthenticate(new(bytes.Buffer), getUID(), "foober", []string{caPamOpt,
 				"group=nosuchgroup"})
 			require.Equal(t, AuthSuccess, r)
+
+			// positive test with authorized_principals_command pam option
+			r = pamAuthenticate(new(bytes.Buffer), getUID(), "foober", []string{caPamOpt,
+				fmt.Sprintf("authorized_principals_command=%s", principalsCommand)})
+			require.Equal(t, AuthSuccess, r)
+
+			// negative test with authorized_principals_command pam option
+			e = ioutil.WriteFile(principalsCommand, []byte("#!/bin/bash\necho 'duber'"), 0555)
+			require.NoError(t, e)
+			r = pamAuthenticate(new(bytes.Buffer), getUID(), "foober", []string{caPamOpt,
+				fmt.Sprintf("authorized_principals_command=%s", principalsCommand)})
+			require.Equal(t, AuthError, r)
+
+			// negative test with bad authorized_principals_command pam option
+			r = pamAuthenticate(new(bytes.Buffer), getUID(), "foober", []string{caPamOpt,
+				"authorized_principals_command=foober"})
+			require.Equal(t, AuthError, r)
 		})
 	})
 }