feat: trusted (instance) domains (#8369)

# Which Problems Are Solved

ZITADEL currently selects the instance context based on a HTTP header
(see https://github.com/zitadel/zitadel/issues/8279#issue-2399959845 and
checks it against the list of instance domains. Let's call it instance
or API domain.
For any context based URL (e.g. OAuth, OIDC, SAML endpoints, links in
emails, ...) the requested domain (instance domain) will be used. Let's
call it the public domain.
In cases of proxied setups, all exposed domains (public domains) require
the domain to be managed as instance domain.
This can either be done using the "ExternalDomain" in the runtime config
or via system API, which requires a validation through CustomerPortal on
zitadel.cloud.

# How the Problems Are Solved

- Two new headers / header list are added:
- `InstanceHostHeaders`: an ordered list (first sent wins), which will
be used to match the instance.
(For backward compatibility: the `HTTP1HostHeader`, `HTTP2HostHeader`
and `forwarded`, `x-forwarded-for`, `x-forwarded-host` are checked
afterwards as well)
- `PublicHostHeaders`: an ordered list (first sent wins), which will be
used as public host / domain. This will be checked against a list of
trusted domains on the instance.
- The middleware intercepts all requests to the API and passes a
`DomainCtx` object with the hosts and protocol into the context
(previously only a computed `origin` was passed)
- HTTP / GRPC server do not longer try to match the headers to instances
themself, but use the passed `http.DomainContext` in their interceptors.
- The `RequestedHost` and `RequestedDomain` from authz.Instance are
removed in favor of the `http.DomainContext`
- When authenticating to or signing out from Console UI, the current
`http.DomainContext(ctx).Origin` (already checked by instance
interceptor for validity) is used to compute and dynamically add a
`redirect_uri` and `post_logout_redirect_uri`.
- Gateway passes all configured host headers (previously only did
`x-zitadel-*`)
- Admin API allows to manage trusted domain

# Additional Changes

None

# Additional Context

- part of #8279 
- open topics: 
  - "single-instance" mode
  - Console UI

proto/zitadel/admin.proto

@@ -323,6 +323,54 @@ service AdminService {
         };
     }
 
+    rpc ListInstanceTrustedDomains(ListInstanceTrustedDomainsRequest) returns (ListInstanceTrustedDomainsResponse) {
+        option (google.api.http) = {
+            post: "/trusted_domains/_search";
+        };
+
+        option (zitadel.v1.auth_option) = {
+            permission: "iam.read";
+        };
+
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+            tags: "Instance";
+            summary: "List Instance Trusted Domains";
+            description: "Returns a list of domains that are configured for this ZITADEL instance. These domains are trusted to be used as public hosts."
+        };
+    }
+
+    rpc AddInstanceTrustedDomain(AddInstanceTrustedDomainRequest) returns (AddInstanceTrustedDomainResponse) {
+        option (google.api.http) = {
+            post: "/trusted_domains";
+        };
+
+        option (zitadel.v1.auth_option) = {
+            permission: "iam.write";
+        };
+
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+            tags: "Instance";
+            summary: "Add an Instance Trusted Domain";
+            description: "Returns a list of domains that are configured for this ZITADEL instance. These domains are trusted to be used as public hosts."
+        };
+    }
+
+    rpc RemoveInstanceTrustedDomain(RemoveInstanceTrustedDomainRequest) returns (RemoveInstanceTrustedDomainResponse) {
+        option (google.api.http) = {
+            delete: "/trusted_domains/{domain}";
+        };
+
+        option (zitadel.v1.auth_option) = {
+            permission: "iam.write";
+        };
+
+        option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation) = {
+            tags: "Instance";
+            summary: "Remove an Instance Trusted Domain";
+            description: "Returns a list of domains that are configured for this ZITADEL instance. These domains are trusted to be used as public hosts."
+        };
+    }
+
     rpc ListSecretGenerators(ListSecretGeneratorsRequest) returns (ListSecretGeneratorsResponse) {
         option (google.api.http) = {
             post: "/secretgenerators/_search"
@@ -4062,6 +4110,52 @@ message ListInstanceDomainsResponse {
     repeated zitadel.instance.v1.Domain result = 3;
 }
 
+message ListInstanceTrustedDomainsRequest {
+    zitadel.v1.ListQuery query = 1;
+    // the field the result is sorted
+    zitadel.instance.v1.DomainFieldName sorting_column = 2;
+    //criteria the client is looking for
+    repeated zitadel.instance.v1.TrustedDomainSearchQuery queries = 3;
+}
+
+message ListInstanceTrustedDomainsResponse {
+    zitadel.v1.ListDetails details = 1;
+    zitadel.instance.v1.DomainFieldName sorting_column = 2;
+    repeated zitadel.instance.v1.TrustedDomain result = 3;
+}
+
+message AddInstanceTrustedDomainRequest {
+    string domain = 1 [
+        (validate.rules).string = {min_len: 1, max_len: 253},
+        (google.api.field_behavior) = REQUIRED,
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"login.example.com\"";
+            min_length: 1;
+            max_length: 253;
+        }
+    ];
+}
+
+message AddInstanceTrustedDomainResponse {
+    zitadel.v1.ObjectDetails details = 1;
+}
+
+message RemoveInstanceTrustedDomainRequest {
+    string domain = 1 [
+        (validate.rules).string = {min_len: 1, max_len: 253},
+        (google.api.field_behavior) = REQUIRED,
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"login.example.com\"";
+            min_length: 1;
+            max_length: 253;
+        }
+    ];
+}
+
+message RemoveInstanceTrustedDomainResponse {
+    zitadel.v1.ObjectDetails details = 1;
+}
+
 message ListSecretGeneratorsRequest {
     //list limitations and ordering
     zitadel.v1.ListQuery query = 1;

proto/zitadel/instance.proto

@@ -163,3 +163,20 @@ enum DomainFieldName {
     DOMAIN_FIELD_NAME_GENERATED = 3;
     DOMAIN_FIELD_NAME_CREATION_DATE = 4;
 }
+
+message TrustedDomain {
+    zitadel.v1.ObjectDetails details = 1;
+    string domain = 2 [
+        (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
+            example: "\"zitadel.com\""
+        }
+    ];
+}
+
+message TrustedDomainSearchQuery {
+    oneof query {
+        option (validate.required) = true;
+
+        DomainQuery domain_query = 1;
+    }
+}