Add TF_ORGANIZATION env var support

TF_ORGANIZATION will serve as a fallback for configuring the organization in the `cloud`
block. This is the first step to make it easier for users wanting to configure Terraform
programmatically.

internal/cloud/backend.go

@@ -113,7 +113,7 @@ func (b *Cloud) ConfigSchema() *configschema.Block {
 			},
 			"organization": {
 				Type:        cty.String,
-				Required:    true,
+				Optional:    true,
 				Description: schemaDescriptionOrganization,
 			},
 			"token": {
@@ -152,8 +152,13 @@ func (b *Cloud) PrepareConfig(obj cty.Value) (cty.Value, tfdiags.Diagnostics) {
 		return obj, diags
 	}
 
+	// check if organization is specified in the config.
 	if val := obj.GetAttr("organization"); val.IsNull() || val.AsString() == "" {
-		diags = diags.Append(invalidOrganizationConfigMissingValue)
+		// organization is specified in the config but is invalid, so
+		// we'll fallback on TF_ORGANIZATION
+		if val := os.Getenv("TF_ORGANIZATION"); val == "" {
+			diags = diags.Append(invalidOrganizationConfigMissingValue)
+		}
 	}
 
 	WorkspaceMapping := WorkspaceMapping{}
@@ -342,8 +347,14 @@ func (b *Cloud) setConfigurationFields(obj cty.Value) tfdiags.Diagnostics {
 		b.hostname = defaultHostname
 	}
 
-	// Get the organization.
-	if val := obj.GetAttr("organization"); !val.IsNull() {
+	// We can have two options, setting the organization via the config
+	// or using TF_ORGANIZATION. Since PrepareConfig() validates that one of these
+	// values must exist, we'll initially set it to the env var and override it if
+	// specified in the configuration.
+	b.organization = os.Getenv("TF_ORGANIZATION")
+
+	// Check if the organization is present and valid in the config.
+	if val := obj.GetAttr("organization"); !val.IsNull() && val.AsString() != "" {
 		b.organization = val.AsString()
 	}
 

internal/cloud/backend_test.go

@@ -146,6 +146,119 @@ func TestCloud_PrepareConfig(t *testing.T) {
 	}
 }
 
+func TestCloud_PrepareConfigWithEnvVars(t *testing.T) {
+	cases := map[string]struct {
+		config      cty.Value
+		vars        map[string]string
+		expectedErr string
+	}{
+		"with no organization": {
+			config: cty.ObjectVal(map[string]cty.Value{
+				"organization": cty.NullVal(cty.String),
+				"workspaces": cty.ObjectVal(map[string]cty.Value{
+					"name": cty.StringVal("prod"),
+					"tags": cty.NullVal(cty.Set(cty.String)),
+				}),
+			}),
+			vars: map[string]string{
+				"TF_ORGANIZATION": "example-org",
+			},
+		},
+		"with no organization attribute or env var": {
+			config: cty.ObjectVal(map[string]cty.Value{
+				"organization": cty.NullVal(cty.String),
+				"workspaces": cty.ObjectVal(map[string]cty.Value{
+					"name": cty.StringVal("prod"),
+					"tags": cty.NullVal(cty.Set(cty.String)),
+				}),
+			}),
+			vars:        map[string]string{},
+			expectedErr: `Invalid organization value: The "organization" attribute value must not be empty.`,
+		},
+	}
+
+	for name, tc := range cases {
+		s := testServer(t)
+		b := New(testDisco(s))
+
+		for k, v := range tc.vars {
+			os.Setenv(k, v)
+			defer os.Unsetenv(k)
+		}
+
+		_, valDiags := b.PrepareConfig(tc.config)
+		if valDiags.Err() != nil && tc.expectedErr != "" {
+			actualErr := valDiags.Err().Error()
+			if !strings.Contains(actualErr, tc.expectedErr) {
+				t.Fatalf("%s: unexpected validation result: %v", name, valDiags.Err())
+			}
+		}
+	}
+}
+
+func TestCloud_configWithEnvVars(t *testing.T) {
+	cases := map[string]struct {
+		config               cty.Value
+		vars                 map[string]string
+		expectedOrganization string
+	}{
+		"with no organization specified": {
+			config: cty.ObjectVal(map[string]cty.Value{
+				"hostname":     cty.NullVal(cty.String),
+				"token":        cty.NullVal(cty.String),
+				"organization": cty.NullVal(cty.String),
+				"workspaces": cty.ObjectVal(map[string]cty.Value{
+					"name": cty.StringVal("prod"),
+					"tags": cty.NullVal(cty.Set(cty.String)),
+				}),
+			}),
+			vars: map[string]string{
+				"TF_ORGANIZATION": "hashicorp",
+			},
+			expectedOrganization: "hashicorp",
+		},
+		"with both organization and env var specified": {
+			config: cty.ObjectVal(map[string]cty.Value{
+				"hostname":     cty.NullVal(cty.String),
+				"token":        cty.NullVal(cty.String),
+				"organization": cty.StringVal("hashicorp"),
+				"workspaces": cty.ObjectVal(map[string]cty.Value{
+					"name": cty.StringVal("prod"),
+					"tags": cty.NullVal(cty.Set(cty.String)),
+				}),
+			}),
+			vars: map[string]string{
+				"TF_ORGANIZATION": "we-should-not-see-this",
+			},
+			expectedOrganization: "hashicorp",
+		},
+	}
+
+	for name, tc := range cases {
+		s := testServer(t)
+		b := New(testDisco(s))
+
+		for k, v := range tc.vars {
+			os.Setenv(k, v)
+			defer os.Unsetenv(k)
+		}
+
+		_, valDiags := b.PrepareConfig(tc.config)
+		if valDiags.Err() != nil {
+			t.Fatalf("%s: unexpected validation result: %v", name, valDiags.Err())
+		}
+
+		diags := b.Configure(tc.config)
+		if diags.Err() != nil {
+			t.Fatalf("%s: unexpected configuration result: %v", name, valDiags.Err())
+		}
+
+		if tc.expectedOrganization != "" && tc.expectedOrganization != b.organization {
+			t.Fatalf("%s: organization not valid: %s, expected: %s", name, b.organization, tc.expectedOrganization)
+		}
+	}
+}
+
 func TestCloud_config(t *testing.T) {
 	cases := map[string]struct {
 		config  cty.Value