govc: sha256 for session cache

Use sha256 for session cache file names

This maintains compatibility between govc and Terraform, allowing
the two to share the same cache while also ensureing SHA1 is eliminated.

Signed-off-by: Ryan Johnson <ryan.johnson@broadcom.com>

session/cache/session.go

@@ -18,7 +18,7 @@ package cache
 
 import (
 	"context"
-	"crypto/sha1"
+	"crypto/sha256"
 	"encoding/json"
 	"fmt"
 	"net/url"
@@ -105,7 +105,7 @@ func (s *Session) key(path string) string {
 	// Key session file off of full URI and insecure setting.
 	// Hash key to get a predictable, canonical format.
 	key := fmt.Sprintf("%s#insecure=%t", p.String(), s.Insecure)
-	return fmt.Sprintf("%040x", sha1.Sum([]byte(key)))
+	return fmt.Sprintf("%064x", sha256.Sum256([]byte(key)))
 }
 
 func (s *Session) file(p string) string {