[chore] combine auth files, rename old names related to authentificat…

…or (#6666)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

extension/auth/default_clientauthenticator.go → extension/auth/client.go

@@ -20,9 +20,21 @@ import (
 	"google.golang.org/grpc/credentials"
 
 	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/extension"
 )
 
-var _ Client = (*defaultClient)(nil)
+// Client is an Extension that can be used as an authenticator for the configauth.Authentication option.
+// Authenticators are then included as part of OpenTelemetry Collector builds and can be referenced by their
+// names from the Authentication configuration.
+type Client interface {
+	extension.Extension
+
+	// RoundTripper returns a RoundTripper that can be used to authenticate HTTP requests.
+	RoundTripper(base http.RoundTripper) (http.RoundTripper, error)
+
+	// PerRPCCredentials returns a PerRPCCredentials that can be used to authenticate gRPC requests.
+	PerRPCCredentials() (credentials.PerRPCCredentials, error)
+}
 
 // ClientOption represents the possible options for NewServerAuthenticator.
 type ClientOption func(*defaultClient)

extension/auth/default_serverauthenticator.go → extension/auth/server.go

@@ -18,9 +18,27 @@ import (
 	"context"
 
 	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/extension"
 )
 
-var _ Server = (*defaultServer)(nil)
+// Server is an Extension that can be used as an authenticator for the configauth.Authentication option.
+// Authenticators are then included as part of OpenTelemetry Collector builds and can be referenced by their
+// names from the Authentication configuration. Each Server is free to define its own behavior and configuration options,
+// but note that the expectations that come as part of Extensions exist here as well. For instance, multiple instances of the same
+// authenticator should be possible to exist under different names.
+type Server interface {
+	extension.Extension
+
+	// Authenticate checks whether the given headers map contains valid auth data. Successfully authenticated calls will always return a nil error.
+	// When the authentication fails, an error must be returned and the caller must not retry. This function is typically called from interceptors,
+	// on behalf of receivers, but receivers can still call this directly if the usage of interceptors isn't suitable.
+	// The deadline and cancellation given to this function must be respected, but note that authentication data has to be part of the map, not context.
+	// The resulting context should contain the authentication data, such as the principal/username, group membership (if available), and the raw
+	// authentication data (if possible). This will allow other components in the pipeline to make decisions based on that data, such as routing based
+	// on tenancy as determined by the group membership, or passing through the authentication data to the next collector/backend.
+	// The context keys to be used are not defined yet.
+	Authenticate(ctx context.Context, headers map[string][]string) (context.Context, error)
+}
 
 type defaultServer struct {
 	ServerAuthenticateFunc