Congressional analysts on President's authority to close the border

The Conressional Research Service has issued a report which may be viewed here.
Some excerpts:

...Federal statutes grant the Department of Homeland Security(DHS)generalauthorityover operations to secure the border and specific authorityto close temporarily “any. . .port of entry” when necessary to protect national interests. Otherstatutesgive the President broad authority to suspend the entry of non-U.S. citizens. Together, these statutes probably authorize a range of targeted executive measuresto close a port of entry or to restrict operations at some ports, at least in some circumstances. Whether the statutes authorize more sweeping executive action to close manyor all of theports of entry on the southernborder to most or all people and goods, however, is a question with which federal courts  have not grappled and which may face significant constitutional and other legal obstacles, depending on the scope of the executive action.
Statutory Bases of Executive Authority
The executive branch possesses two types of statutory authority that it might leverage in support of a decision to restrict or suspend the entry of goods or people at ports of entry on thesouthern border.First,some statutes supply executive agencies with authority over border operations. Perhaps most relevantis 19 U.S.C. § 1318(b)(2), which provides as follows:
[T]he Commissioner of U.S. Customs and Border Protection, when necessary to respond to a specific threat to human life or national interests, is authorized to close temporarily any Customs office or port of entry or take any other lesser action that may be necessary to respond to the specific threat.
More generally, the Homeland Security Act makes the Secretary of Homeland Security responsible for “[s]ecuring the borders, territorial waters, ports, terminals, waterways, and air, land, and sea transportation systems of the United States, including managing and coordinating those functions transferred to the Department at ports of entry.” A provision of the Immigration and Nationality Act (INA), somewhat similarly, grants the Secretary “the power and duty to control and guard the boundaries and borders of the United States against the illegal entry of aliens.”However, the INA also directs DHS to follow certain inspection procedures, including for asylum seekers who lack valid entry documents,and constitutional principles grant U.S. citizens and lawful permanent residents (LPRs) certain rights with respect to reentering the country, as discussed further below.
Second, other statutes grant the executive branch broad authority to restrict the entry of aliens. INA § 212(f), which came to public attention when President Trump invokedit as authority for the “Travel Ban” executive orders and proclamation, confers exceptionally broad power on the President in this regard:
Whenever the President finds that the entry of any aliens or of any class of aliens into the United States would be detrimental to the interests of the United States, he may by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate.
Another statute, also cited in the Travel Ban orders and proclamation, allows the President to restrict the entry of aliens according to “such reasonable rules, regulations, and orders, and subject to such limitations and exceptions as the President may prescribe.” In Trump v. Hawaii, which upheld the Travel Ban proclamationas a valid exercise of the President’s authority under INA § 212(f), the Supreme Court reasoned that the statute “exudes deference to the President” and “vests[him]with ‘ample power’to impose entry restrictions in addition to those elsewhere enumerated in the INA.”The Court also emphasized that presidential determinations related to national security traditionally receive deference and declined to probe the national security justifications that the President gave for the proclamation’s entry restrictions on broad categories of nationals of seven countries.