[receiver/solace]: Update the auth validation step (#36386)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

The validation step should not allow configuring several auth methods
when only one will be considered (the first one that's not nil in this
order plain > xauth2 > external).

(technically this is a breaking change because some users might have
several auth methods configured, but that doesn't make sense so it's
unlikely to break many users if any)

<!--Describe what testing was performed and which tests were added.-->
#### Testing
One test with multiple auth methods was added.

---------

Co-authored-by: Daniel Jaglowski <[email protected]>
Co-authored-by: Antoine Toulme <[email protected]>

.chloggen/solace-receiver-validation-improvements.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: solacereceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Update validation step to allow only one auth method.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [36386]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/solacereceiver/config.go

@@ -19,6 +19,7 @@ const (
 
 var (
 	errMissingAuthDetails       = errors.New("authentication details are required, either for plain user name password or XOAUTH2 or client certificate")
+	errTooManyAuthDetails       = errors.New("only one authentication method must be used")
 	errMissingQueueName         = errors.New("queue definition is required, queue definition has format queue://<queuename>")
 	errMissingPlainTextParams   = errors.New("missing plain text auth params: Username, Password")
 	errMissingXauth2Params      = errors.New("missing xauth2 text auth params: Username, Bearer")
@@ -46,9 +47,22 @@ type Config struct {
 
 // Validate checks the receiver configuration is valid
 func (cfg *Config) Validate() error {
-	if cfg.Auth.PlainText == nil && cfg.Auth.External == nil && cfg.Auth.XAuth2 == nil {
+	authMethod := 0
+	if cfg.Auth.PlainText != nil {
+		authMethod++
+	}
+	if cfg.Auth.External != nil {
+		authMethod++
+	}
+	if cfg.Auth.XAuth2 != nil {
+		authMethod++
+	}
+	if authMethod == 0 {
 		return errMissingAuthDetails
 	}
+	if authMethod > 1 {
+		return errTooManyAuthDetails
+	}
 	if len(strings.TrimSpace(cfg.Queue)) == 0 {
 		return errMissingQueueName
 	}

receiver/solacereceiver/config_test.go

@@ -87,6 +87,15 @@ func TestConfigValidateMissingAuth(t *testing.T) {
 	assert.Equal(t, errMissingAuthDetails, err)
 }
 
+func TestConfigValidateMultipleAuth(t *testing.T) {
+	cfg := createDefaultConfig().(*Config)
+	cfg.Queue = "someQueue"
+	cfg.Auth.PlainText = &SaslPlainTextConfig{"Username", "Password"}
+	cfg.Auth.XAuth2 = &SaslXAuth2Config{"Username", "Bearer"}
+	err := component.ValidateConfig(cfg)
+	assert.Equal(t, errTooManyAuthDetails, err)
+}
+
 func TestConfigValidateMissingQueue(t *testing.T) {
 	cfg := createDefaultConfig().(*Config)
 	cfg.Auth.PlainText = &SaslPlainTextConfig{"Username", "Password"}