diff --git a/R/AzureSMRbase.R b/R/AzureSMRbase.R
new file mode 100644
index 0000000..b693102
--- /dev/null
+++ b/R/AzureSMRbase.R
@@ -0,0 +1,6 @@
+.onLoad <- function(libname, pkgname)
+{
+    azure_api_version="2018-05-01"
+    options(azure_api_version=azure_api_version)
+    invisible(NULL)
+}
diff --git a/R/az_auth.R b/R/az_auth.R
index fa1c8ad..7111c64 100644
--- a/R/az_auth.R
+++ b/R/az_auth.R
@@ -68,9 +68,9 @@ private=list(
     # obtain subscription IDs owned by this app
     set_subs=function()
     {
-        cont <- call_azure_sm(private$token, subscription="", operation="", api_version="2016-06-01")
+        cont <- call_azure_sm(private$token, subscription="", operation="")
 
-        df <- lapply(cont, data.frame, stringsAsFactors=FALSE)
+        df <- lapply(cont$value, data.frame, stringsAsFactors=FALSE)
         df <- do.call(rbind, df)
 
         # update subscription IDs; notify if more than one found
diff --git a/R/az_resgroup.R b/R/az_resgroup.R
index 10553c8..8cc74ef 100644
--- a/R/az_resgroup.R
+++ b/R/az_resgroup.R
@@ -18,7 +18,7 @@ public=list(
         self$name <- name
 
         op <- paste0("resourcegroups/", self$name)
-        cont <- call_azure_sm(private$token, self$subscription, operation=op, api_version="2018-05-01")
+        cont <- call_azure_sm(private$token, self$subscription, op)
         self$id <- cont$id
         self$location <- cont$location
         self$managed_by <- cont$managedBy
@@ -40,7 +40,7 @@ private=list(
     set_res=function()
     {
         op <- paste0("resourcegroups/", self$name, "/resources")
-        cont <- call_azure_sm(private$token, self$subscription, operation=op, api_version="2018-05-01")
+        cont <- call_azure_sm(private$token, self$subscription, op)
         self$resources <- sapply(cont$value, `[[`, "name")
         NULL
     }
diff --git a/R/az_subscription.R b/R/az_subscription.R
index c727dda..6ffd613 100644
--- a/R/az_subscription.R
+++ b/R/az_subscription.R
@@ -14,7 +14,7 @@ public=list(
     {
         private$token <- token
         self$id <- id
-        info <- call_azure_sm(token, id, "", api_version="2018-05-01")
+        info <- call_azure_sm(token, id, "")
         self$name <- info$displayName
         self$state <- info$state
         self$policies <- info$subscriptionPolicies
@@ -44,7 +44,7 @@ private=list(
     token=NULL,
     set_rgrps=function()
     {
-        cont <- call_azure_sm(private$token, self$id, operation="resourcegroups", api_version="2018-05-01")
+        cont <- call_azure_sm(private$token, self$id, "resourcegroups")
         self$resource_groups <- sapply(cont$value, `[[`, "name")
         NULL
     }
diff --git a/R/call_azure_sm.R b/R/call_azure_sm.R
index 6631d2c..ea7ae9b 100644
--- a/R/call_azure_sm.R
+++ b/R/call_azure_sm.R
@@ -1,9 +1,11 @@
-call_azure_sm <- function(token, subscription, operation, api_version,
+call_azure_sm <- function(token, subscription, operation, api_version=getOption("azure_api_version"),
                           http_verb=c("GET", "DELETE", "PUT", "POST", "HEAD"),
                           catch=c("stop", "warn", "message", "pass"), ...)
 {
     creds <- token$credentials
 
+    # TODO: if token has expired, renew it
+
     url <- httr::parse_url(creds$resource)
     url$path <- file.path("subscriptions", subscription, operation, fsep="/")
     url$query <- list(`api-version`=api_version)