Add migration exchange method (#24)

migration.go

@@ -0,0 +1,35 @@
+package slack
+
+import (
+	"context"
+	"net/url"
+)
+
+type migrationExchangeResponseFull struct {
+	TeamID         string            `json:"team_id"`
+	EnterpriseID   string            `json:"enterprise_id"`
+	UserIDMap      map[string]string `json:"user_id_map"`
+	InvalidUserIDs []string          `json:"invalid_user_ids"`
+	SlackResponse
+}
+
+// MigrationExchange for Enterprise Grid workspaces, map local user IDs to global user IDs
+func (api *Client) MigrationExchange(ctx context.Context, teamID string, users []string) (map[string]string, error) {
+	values := url.Values{
+		"users": users,
+	}
+	if teamID != "" {
+		values.Add("team_id", teamID)
+	}
+	response := &migrationExchangeResponseFull{}
+	err := api.getMethod(ctx, "migration.exchange", api.token, values, response)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := response.Err(); err != nil {
+		return nil, err
+	}
+
+	return response.UserIDMap, nil
+}