Add the get-tokens command

internal/cli/get_token.go

@@ -40,9 +40,19 @@ Fetch an access token for the given client and API.
 				return err
 			}
 
-			// TODO: We can check here if the client is an m2m client, and if so
+			// We can check here if the client is an m2m client, and if so
 			// initiate the client credentials flow instead to fetch a token,
 			// avoiding the browser and HTTP server shenanigans altogether.
+			if client.GetAppType() == "non_interactive" {
+				tokenResponse, err := runClientCredentialsFlow(cli, client, clientID, audience)
+				if err != nil {
+					return err
+				}
+
+				fmt.Fprint(cli.renderer.MessageWriter, "\n")
+				cli.renderer.GetToken(client, tokenResponse)
+				return nil
+			}
 
 			if proceed := runLoginFlowPreflightChecks(cli, client); !proceed {
 				return nil

internal/cli/utils_shared.go

@@ -3,12 +3,15 @@ package cli
 import (
 	"fmt"
 
+	"encoding/json"
 	"github.com/auth0/auth0-cli/internal/ansi"
 	"github.com/auth0/auth0-cli/internal/auth/authutil"
 	"github.com/auth0/auth0-cli/internal/auth0"
 	"github.com/auth0/auth0-cli/internal/open"
 	"github.com/auth0/auth0-cli/internal/prompt"
 	"gopkg.in/auth0.v5/management"
+	"net/http"
+	"strings"
 )
 
 const (
@@ -23,6 +26,52 @@ var (
 	cliLoginTestingScopes []string = []string{"openid", "profile"}
 )
 
+// runClientCredentialsFlow runs an M2M client credentials flow without opening a browser
+func runClientCredentialsFlow(cli *cli, c *management.Client, clientID string, audience string) (*authutil.TokenResponse, error) {
+
+	var tokenResponse *authutil.TokenResponse
+
+	tenant, err := cli.getTenant()
+	if err != nil {
+		return tokenResponse, err
+	}
+
+	url := "https://" + tenant.Domain + "/oauth/token"
+
+	cli.renderer.Infof("Domain:   " + tenant.Domain)
+	cli.renderer.Infof("ClientID: " + clientID)
+	cli.renderer.Infof("Type:     Machine to Machine")
+	fmt.Println()
+
+	client_secret := c.GetClientSecret()
+
+	// TODO: Check if the audience is valid, and suggest a different client if it is wrong.
+
+	payload := strings.NewReader("grant_type=client_credentials&client_id=" + clientID + "&client_secret=" + client_secret + "&audience=" + audience)
+
+	err = ansi.Spinner("Waiting for token", func() error {
+		req, _ := http.NewRequest("POST", url, payload)
+
+		req.Header.Add("content-type", "application/x-www-form-urlencoded")
+
+		res, err := http.DefaultClient.Do(req)
+
+		if err != nil {
+			return err
+		}
+
+		defer res.Body.Close()
+
+		err = json.NewDecoder(res.Body).Decode(&tokenResponse)
+		if err != nil {
+			return fmt.Errorf("cannot decode response: %w", err)
+		}
+		return nil
+	})
+
+	return tokenResponse, err
+}
+
 // runLoginFlowPreflightChecks checks if we need to make any updates to the
 // client being tested in order to log in successfully. If so, it asks the user
 // to confirm whether to proceed.