Add basic daemon mode loop

Signed-off-by: Noah Stride <noah.stride@goteleport.com>

cmd/main.go

@@ -1,10 +1,12 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"log/slog"
 	"os"
+	"time"
 
 	"github.com/spf13/cobra"
 	awsspiffe "github.com/spiffe/aws-spiffe-workload-helper"
@@ -120,6 +122,176 @@ func exchangeX509SVIDForAWSCredentials(
 	return credentials, nil
 }
 
+func oneshotX509CredentialFile(
+	ctx context.Context,
+	force bool,
+	replace bool,
+	awsCredentialsPath string,
+	sf *sharedFlags,
+) error {
+	client, err := workloadapi.New(
+		ctx,
+		workloadapi.WithAddr(sf.workloadAPIAddr),
+	)
+	if err != nil {
+		return fmt.Errorf("creating workload api client: %w", err)
+	}
+	defer func() {
+		if err := client.Close(); err != nil {
+			slog.Warn("Failed to close workload API client", "error", err)
+		}
+	}()
+
+	x509Ctx, err := client.FetchX509Context(ctx)
+	if err != nil {
+		return fmt.Errorf("fetching x509 context: %w", err)
+	}
+	svid := x509Ctx.DefaultSVID()
+	slog.Debug(
+		"Fetched X509 SVID",
+		slog.Group("svid",
+			"spiffe_id", svid.ID,
+			"hint", svid.Hint,
+		),
+	)
+
+	credentials, err := exchangeX509SVIDForAWSCredentials(sf, svid)
+	if err != nil {
+		return fmt.Errorf("exchanging X509 SVID for AWS credentials: %w", err)
+	}
+
+	// Now we write this to disk in the format that the AWS CLI/SDK
+	// expects for a credentials file.
+	err = internal.UpsertAWSCredentialsFileProfile(
+		slog.Default(),
+		internal.AWSCredentialsFileConfig{
+			Path:        awsCredentialsPath,
+			Force:       force,
+			ReplaceFile: replace,
+		},
+		internal.AWSCredentialsFileProfile{
+			AWSAccessKeyID:     credentials.AccessKeyId,
+			AWSSecretAccessKey: credentials.SecretAccessKey,
+			AWSSessionToken:    credentials.SessionToken,
+		},
+	)
+	if err != nil {
+		return fmt.Errorf("writing credentials to file: %w", err)
+	}
+	slog.Info("Wrote AWS credential to file", "path", "./my-credential")
+	return nil
+}
+
+func daemonX509CredentialFile(
+	ctx context.Context,
+	force bool,
+	replace bool,
+	awsCredentialsPath string,
+	sf *sharedFlags,
+) error {
+	slog.Info("Starting AWS credential file daemon")
+	client, err := workloadapi.New(
+		ctx,
+		workloadapi.WithAddr(sf.workloadAPIAddr),
+	)
+	if err != nil {
+		return fmt.Errorf("creating workload api client: %w", err)
+	}
+	defer func() {
+		if err := client.Close(); err != nil {
+			slog.Warn("Failed to close workload API client", "error", err)
+		}
+	}()
+
+	slog.Debug("Fetching initial X509 SVID")
+	x509Source, err := workloadapi.NewX509Source(ctx, workloadapi.WithClient(client))
+	if err != nil {
+		return fmt.Errorf("creating x509 source: %w", err)
+	}
+	defer func() {
+		if err := x509Source.Close(); err != nil {
+			slog.Warn("Failed to close x509 source", "error", err)
+		}
+	}()
+
+	svidUpdate := x509Source.Updated()
+	svid, err := x509Source.GetX509SVID()
+	if err != nil {
+		return fmt.Errorf("fetching initial X509 SVID: %w", err)
+	}
+	slog.Debug("Fetched initial X509 SVID", slog.Group("svid",
+		"spiffe_id", svid.ID,
+		"hint", svid.Hint,
+		"expires_at", svid.Certificates[0].NotAfter,
+	))
+
+	for {
+		slog.Debug("Exchanging X509 SVID for AWS credentials")
+		credentials, err := exchangeX509SVIDForAWSCredentials(sf, svid)
+		if err != nil {
+			return fmt.Errorf("exchanging X509 SVID for AWS credentials: %w", err)
+		}
+		slog.Info(
+			"Successfully exchanged X509 SVID for AWS credentials",
+		)
+
+		expiresAt, err := time.Parse(time.RFC3339, credentials.Expiration)
+		if err != nil {
+			return fmt.Errorf("parsing expiration time: %w", err)
+		}
+
+		slog.Debug("Writing AWS credentials to file", "path", awsCredentialsPath)
+		err = internal.UpsertAWSCredentialsFileProfile(
+			slog.Default(),
+			internal.AWSCredentialsFileConfig{
+				Path:        awsCredentialsPath,
+				Force:       force,
+				ReplaceFile: replace,
+			},
+			internal.AWSCredentialsFileProfile{
+				AWSAccessKeyID:     credentials.AccessKeyId,
+				AWSSecretAccessKey: credentials.SecretAccessKey,
+				AWSSessionToken:    credentials.SessionToken,
+			},
+		)
+		if err != nil {
+			return fmt.Errorf("writing credentials to file: %w", err)
+		}
+		slog.Info("Wrote AWS credentials to file", "path", awsCredentialsPath)
+
+		slog.Info(
+			"Sleeping until a new X509 SVID is received or the AWS credentials are close to expiry",
+			"aws_expires_at", expiresAt,
+			"aws_ttl", expiresAt.Sub(time.Now()),
+			"svid_expires_at", svid.Certificates[0].NotAfter,
+			"svid_ttl", svid.Certificates[0].NotAfter.Sub(time.Now()),
+		)
+		select {
+		case <-time.After(time.Second * 10):
+			slog.Info("Triggering renewal as AWS credentials are close to expiry")
+		// TODO: Add case for AWS credential approaching expiry
+		case <-svidUpdate:
+			slog.Debug("Received potential X509 SVID update")
+			newSVID, err := x509Source.GetX509SVID()
+			if err != nil {
+				return fmt.Errorf("fetching updated X509 SVID: %w", err)
+			}
+			slog.Info(
+				"Received new X509 SVID from Workload API, will update AWS credentials",
+				slog.Group("svid",
+					"spiffe_id", newSVID.ID,
+					"hint", newSVID.Hint,
+					"expires_at", newSVID.Certificates[0].NotAfter,
+				),
+			)
+			svid = newSVID
+		case <-ctx.Done():
+			return nil
+		}
+	}
+
+}
+
 func newX509CredentialFileCmd() (*cobra.Command, error) {
 	oneshot := false
 	force := false
@@ -131,53 +303,14 @@ func newX509CredentialFileCmd() (*cobra.Command, error) {
 		Short: ``,
 		Long:  ``,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			ctx := cmd.Context()
-			client, err := workloadapi.New(
-				ctx,
-				workloadapi.WithAddr(sf.workloadAPIAddr),
-			)
-			if err != nil {
-				return fmt.Errorf("creating workload api client: %w", err)
-			}
-
-			x509Ctx, err := client.FetchX509Context(ctx)
-			if err != nil {
-				return fmt.Errorf("fetching x509 context: %w", err)
-			}
-			svid := x509Ctx.DefaultSVID()
-			slog.Debug(
-				"Fetched X509 SVID",
-				slog.Group("svid",
-					"spiffe_id", svid.ID,
-					"hint", svid.Hint,
-				),
-			)
-
-			credentials, err := exchangeX509SVIDForAWSCredentials(sf, svid)
-			if err != nil {
-				return fmt.Errorf("exchanging X509 SVID for AWS credentials: %w", err)
+			if oneshot {
+				return oneshotX509CredentialFile(
+					cmd.Context(), force, replace, awsCredentialsPath, sf,
+				)
 			}
-
-			// Now we write this to disk in the format that the AWS CLI/SDK
-			// expects for a credentials file.
-			err = internal.UpsertAWSCredentialsFileProfile(
-				slog.Default(),
-				internal.AWSCredentialsFileConfig{
-					Path:        awsCredentialsPath,
-					Force:       force,
-					ReplaceFile: replace,
-				},
-				internal.AWSCredentialsFileProfile{
-					AWSAccessKeyID:     credentials.AccessKeyId,
-					AWSSecretAccessKey: credentials.SecretAccessKey,
-					AWSSessionToken:    credentials.SessionToken,
-				},
+			return daemonX509CredentialFile(
+				cmd.Context(), force, replace, awsCredentialsPath, sf,
 			)
-			if err != nil {
-				return fmt.Errorf("writing credentials to file: %w", err)
-			}
-			slog.Info("Wrote AWS credential to file", "path", "./my-credential")
-			return nil
 		},
 		// Hidden for now as the daemon is likely more "usable"
 		Hidden: true,
@@ -211,6 +344,11 @@ func newX509CredentialProcessCmd() (*cobra.Command, error) {
 			if err != nil {
 				return fmt.Errorf("creating workload api client: %w", err)
 			}
+			defer func() {
+				if err := client.Close(); err != nil {
+					slog.Warn("Failed to close workload API client", "error", err)
+				}
+			}()
 
 			x509Ctx, err := client.FetchX509Context(ctx)
 			if err != nil {