Fix for issue 3797.

Docker's logic for resolving credentials from .dockercfg accepts two kinds of matches:
1. an exact match between the dockercfg entry and the image prefix
2. a hostname match between the dockercfg entry and the image prefix

This change implements the latter, which permits the docker client to take .dockercfg entries of the form:
   https://quay.io/v1/
and use them for images of the form:
   quay.io/foo/bar
even though they are not a prefix-match.

pkg/credentialprovider/keyring.go

@@ -66,9 +66,20 @@ func (dk *BasicDockerKeyring) Add(cfg DockerConfig) {
 			continue
 		}
 
-		registry := parsed.Host + parsed.Path
-		dk.creds[registry] = creds
-		dk.index = append(dk.index, registry)
+		// The docker client allows exact matches:
+		//    foo.bar.com/namespace
+		// Or hostname matches:
+		//    foo.bar.com
+		// See ResolveAuthConfig in docker/registry/auth.go.
+		if parsed.Host != "" {
+			// NOTE: foo.bar.com comes through as Path.
+			dk.creds[parsed.Host] = creds
+			dk.index = append(dk.index, parsed.Host)
+		}
+		if parsed.Path != "/" {
+			dk.creds[parsed.Host+parsed.Path] = creds
+			dk.index = append(dk.index, parsed.Host+parsed.Path)
+		}
 	}
 
 	// Update the index used to identify which credentials to use for a given

pkg/kubelet/dockertools/docker_test.go

@@ -262,6 +262,50 @@ func TestDockerKeyringLookup(t *testing.T) {
 	}
 }
 
+// This validates that dockercfg entries with a scheme and url path are properly matched
+// by images that only match the hostname.
+// NOTE: the above covers the case of a more specific match trumping just hostname.
+func TestIssue3797(t *testing.T) {
+	rex := docker.AuthConfiguration{
+		Username: "rex",
+		Password: "tiny arms",
+		Email:    "rex@example.com",
+	}
+
+	dk := &credentialprovider.BasicDockerKeyring{}
+	dk.Add(credentialprovider.DockerConfig{
+		"https://quay.io/v1/": credentialprovider.DockerConfigEntry{
+			Username: rex.Username,
+			Password: rex.Password,
+			Email:    rex.Email,
+		},
+	})
+
+	tests := []struct {
+		image string
+		match docker.AuthConfiguration
+		ok    bool
+	}{
+		// direct match
+		{"quay.io", rex, true},
+
+		// partial matches
+		{"quay.io/foo", rex, true},
+		{"quay.io/foo/bar", rex, true},
+	}
+
+	for i, tt := range tests {
+		match, ok := dk.Lookup(tt.image)
+		if tt.ok != ok {
+			t.Errorf("case %d: expected ok=%t, got %t", i, tt.ok, ok)
+		}
+
+		if !reflect.DeepEqual(tt.match, match) {
+			t.Errorf("case %d: expected match=%#v, got %#v", i, tt.match, match)
+		}
+	}
+}
+
 type imageTrackingDockerClient struct {
 	*FakeDockerClient
 	imageName string