Add support for mutual authentication via TLS (#459)

Prior to this change, there was no way to pass in a client certificate
if you had set up Nexus behind a load balancer with mutual auth
configured.

This change exposes some new configuration values that allow you to pass
in a path to a file on disk containing your client key/cert (which can
be in a single file) and optionally a Root CA.

README.md

@@ -27,13 +27,34 @@ Implemented and tested with Sonatype Nexus `3.70.1-02`.
 
 ```hcl
 provider "nexus" {
-  insecure = true
-  password = "admin123"
-  url      = "https://127.0.0.1:8080"
-  username = "admin"
+  insecure         = true
+  password         = "admin123"
+  url              = "https://127.0.0.1:8080"
+  username         = "admin"
 }
 ```
 
+Optionally with mTLS if Nexus is deployed behind a reverse proxy:
+
+```hcl
+provider "nexus" {
+  insecure         = true
+  password         = "admin123"
+  url              = "https://127.0.0.1:8080"
+  username         = "admin"
+  client_cert_path = "/path/to/client.crt"
+  client_key_path  = "/path/to/client.key"
+  root_ca_path     = "/path/to/root_ca.crt"
+}
+```
+
+Note that the `root_ca_path` should contain ALL certificates required for 
+communication. It overrides the system CA store, rather than adding to it.
+
+You can point the `root_ca_path` to the system trust store if required, e.g.:
+
+`root_ca_path = "/etc/ssl/certs/ca-certificates.crt"`
+
 ## Development
 
 ### Build

internal/provider/main.go

@@ -178,19 +178,43 @@ func Provider() *schema.Provider {
 				Optional:    true,
 				Type:        schema.TypeInt,
 			},
+			"client_cert_path": {
+				Description: "Path to a client PEM certificate to load for mTLS. Reading environment variable NEXUS_CLIENT_CERT_PATH. Default:``",
+				DefaultFunc: schema.EnvDefaultFunc("NEXUS_CLIENT_CERT_PATH", ""),
+				Optional:    true,
+				Type:        schema.TypeString,
+			},
+			"client_key_path": {
+				Description: "Path to a client PEM key to load for mTLS. Reading environment variable NEXUS_CLIENT_KEY_PATH. Default:``",
+				DefaultFunc: schema.EnvDefaultFunc("NEXUS_CLIENT_KEY_PATH", ""),
+				Optional:    true,
+				Type:        schema.TypeString,
+			},
+			"root_ca_path": {
+				Description: "Path to a root CA certificate to load for mTLS. Reading environment variable NEXUS_ROOT_CA_PATH. Default:``",
+				DefaultFunc: schema.EnvDefaultFunc("NEXUS_ROOT_CA_PATH", ""),
+				Optional:    true,
+				Type:        schema.TypeString,
+			},
 		},
 		ConfigureFunc: providerConfigure,
 	}
 }
 
 func providerConfigure(d *schema.ResourceData) (interface{}, error) {
 	timeout := d.Get("timeout").(int)
+	clientCertPath := d.Get("client_cert_path").(string)
+	clientKeyPath := d.Get("client_key_path").(string)
+	rootCaPath := d.Get("root_ca_path").(string)
 	config := client.Config{
-		Insecure: d.Get("insecure").(bool),
-		Password: d.Get("password").(string),
-		URL:      d.Get("url").(string),
-		Username: d.Get("username").(string),
-		Timeout:  &timeout,
+		Insecure:              d.Get("insecure").(bool),
+		Password:              d.Get("password").(string),
+		URL:                   d.Get("url").(string),
+		Username:              d.Get("username").(string),
+		Timeout:               &timeout,
+		ClientCertificatePath: &clientCertPath,
+		ClientKeyPath:         &clientKeyPath,
+		RootCAPath:            &rootCaPath,
 	}
 
 	return nexus.NewClient(config), nil