provider: add configuration option to use a specific base_url

Following on from cloudflare/cloudflare-go#606, this allows the provider
to pass through the ability to override the base URL that the API client
uses for calls.

.changelog/1270.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+provider: add the ability to configure a different base URL for the API client
+```

cloudflare/provider.go

@@ -89,6 +89,13 @@ func Provider() *schema.Provider {
 				DefaultFunc: schema.EnvDefaultFunc("CLOUDFLARE_ACCOUNT_ID", nil),
 				Description: "Configure API client to always use that account",
 			},
+
+			"base_url": {
+				Type:        schema.TypeString,
+				Optional:    true,
+				DefaultFunc: schema.EnvDefaultFunc("CLOUDFLARE_BASE_URL", "https://api.cloudflare.com/client/v4"),
+				Description: "Configure the base URL used by the API client",
+			},
 		},
 
 		DataSourcesMap: map[string]*schema.Resource{
@@ -183,9 +190,10 @@ func Provider() *schema.Provider {
 }
 
 func providerConfigure(d *schema.ResourceData, terraformVersion string) (interface{}, error) {
+	baseURL := cloudflare.BaseURL(d.Get("base_url").(string))
 	limitOpt := cloudflare.UsingRateLimit(float64(d.Get("rps").(int)))
 	retryOpt := cloudflare.UsingRetryPolicy(d.Get("retries").(int), d.Get("min_backoff").(int), d.Get("max_backoff").(int))
-	options := []cloudflare.Option{limitOpt, retryOpt}
+	options := []cloudflare.Option{limitOpt, retryOpt, baseURL}
 
 	if d.Get("api_client_logging").(bool) {
 		options = append(options, cloudflare.UsingLogger(log.New(os.Stderr, "", log.LstdFlags)))

website/docs/index.html.markdown

@@ -77,3 +77,4 @@ The following arguments are supported:
 * `account_id` - (Optional) Configure API client with this account ID, so calls use the account API rather than the (default) user API.
   This is required for other users in your account to have access to the resources you manage.
   This can also be specified with the `CLOUDFLARE_ACCOUNT_ID` shell environment variable.
+* `base_url` - (Optional) Configure the API client to use a specific base URL. Default: "https://api.cloudflare.com"